WO2016024636A1

WO2016024636A1 - Magnetic force microscope probe for measuring ferromagnetic field and measuring magnetic field value, and method and device for observing magnetic field of ferromagnetic-field-emitting sample

Info

Publication number: WO2016024636A1
Application number: PCT/JP2015/072969
Authority: WO
Inventors: 準齊藤; 哲吉村; 幸則木下
Original assignee: 国立大学法人秋田大学
Priority date: 2014-08-15
Filing date: 2015-08-14
Publication date: 2016-02-18
Also published as: JPWO2016024636A1; JP6624737B2

Abstract

　Provided are: (1) a magnetic force microscope probe provided with at least one magnetic material, the magnetic material being such that, over a temperature range of at least 10-30°C, saturation magnetization is not reached when a magnetic field is applied, the magnetic material being (a) a solid solution of one or more ferromagnetic elements and one or more non-magnetic elements, (b) an amorphous magnetic material containing one or more strongly ferromagnetic elements and one or more non-magnetic elements, or (c) a magnetic material containing one or more types of ferromagnetic particles and one or more non-magnetic materials, the magnetic material being structured such that the ferromagnetic particles are dispersed within and supported by the non-magnetic material; (2) a device for observing a magnetic field, the device being provided with the magnetic force microscope probe of (1); and (3) a method for observing a magnetic field, the method employing the magnetic force microscope probe of (1).

Description

Magnetic force microscope probe for strong magnetic field measurement and magnetic field value measurement, and magnetic field observation method and apparatus for strong magnetic field generation sample

The present invention relates to a probe for use in a magnetic force microscope. The present invention also relates to a method and apparatus for observing the surface magnetic field of a magnetic sample (for example, a permanent magnet) that generates a strong DC magnetic field.

A magnetic force microscope (MFM) is known as a device for measuring a magnetization pattern corresponding to magnetic information of a magnetic sample. The magnetic force microscope is provided with a magnetic probe, the tip of the magnetic probe is brought close to the magnetic sample to be observed, and the magnetic interaction between the magnetic moment of the magnetic probe and the magnetic sample is measured. By detecting the action, the magnetization pattern and the like are measured.

As a magnetic probe for a magnetic force microscope, a cobalt (Co) -chromium (Cr) -based alloy, nickel (Ni) -iron (Fe) -based alloy, cobalt (Co) is formed on a probe material made of a non-magnetic material Si. Generally, a thin film of a ferromagnetic material such as a platinum (Pt) based alloy, an iron (Fe) -platinum (Pt) based ordered alloy, or an iron (Fe) based alloy is formed (Patent Documents 1 to 3).

The present inventors have developed an alternating magnetic force microscope (Patent Documents 4 and 5) in order to observe a magnetic field generated from a magnetic sample with high spatial resolution. These alternating magnetic force microscopes change the magnetization direction of a ferromagnetic probe provided at the tip of an excited cantilever by an external AC magnetic field, and magnetize between the probe magnetization and the magnetic sample magnetic field. By detecting the frequency modulation that occurs in the probe vibration due to the alternating magnetic force generated by the dynamic interaction, it is possible to observe the DC magnetic field gradient or AC magnetic field gradient near the sample surface, and realize high spatial resolution.

Patent Document 4 discloses a magnetic field observation apparatus capable of measuring a magnetic force with high spatial resolution near the surface of a magnetic sample (for example, a magnetic recording medium used in a magnetic storage device) that generates a DC magnetic field. A probe having a magnetic moment that is easy to reverse; an excitation mechanism that excites the probe; a scanning mechanism that causes the probe to scan a magnetic sample; and a magnetic material that can periodically reverse the magnetization of the probe; AC magnetic field generation mechanism for applying an AC magnetic field of a non-resonant frequency different from the cantilever resonance frequency to the probe in a size that does not reverse the magnetization of the sample; and the magnetization of the probe whose magnetization direction is periodically changed by the AC magnetic field This occurs when the apparent spring constant of the probe changes due to the alternating force of the non-resonant frequency applied to the probe due to the magnetic interaction with the magnetization of the magnetic sample. A modulation measurement mechanism capable of measuring the degree of periodic frequency modulation of the vibration of the probe by frequency demodulation; the modulation measurement mechanism is obtained from the sensor that detects the displacement of the probe; An FM demodulator for demodulating the frequency modulation signal, and measuring the magnetic field gradient of the DC magnetic field leaking from the magnetic sample from the frequency demodulated signal obtained from the FM demodulator and the voltage signal of the AC magnetic field generation mechanism. A magnetic field observation apparatus is disclosed.

In Patent Document 5, the vibration of the cantilever is detected while scanning the scanning region on the surface of the observation sample with a probe made of a ferromagnetic material at the tip of the excited cantilever, and the magnetic field in the operation region is detected based on the detection result. A magnetic field profile measuring device for generating a distribution image; a cantilever having a tip attached to a tip; an exciter for exciting the cantilever at a resonance frequency thereof or a frequency close to the frequency; and an AC magnetic field to generate a probe An AC magnetic field generator that frequency-modulates or simultaneously amplitude-modulates the excitation vibration of the cantilever by periodically reversing the magnetic polarity; a vibration sensor that detects the vibration of the probe; and a probe from the detection signal of the vibration sensor While demodulating the magnetic signal corresponding to the alternating magnetic force generated between the sample and the observation sample, the demodulated magnetic signals are orthogonal to each other by 90 ° in phase. A demodulation processing device for detecting the amplitude and phase of the magnetic field at the position of the probe from the demodulated magnetic signal separately detected by two signal components; and a scanning mechanism for scanning the operation region by the probe; The two signal components orthogonal to each other at each coordinate of the operation region or the amplitude and phase of the magnetic field obtained by scanning the operation region with a scanning mechanism under conditions synchronized with the operation of the AC magnetic field generator A data storage device that stores the initial data from the data storage device, and a change data generator that generates a plurality of data in which the phase of the initial data is changed; and each of the operation areas generated by the change data generator An image display device that displays a magnetic field distribution image based on data in coordinates is disclosed.

JP 2008-209276 A JP 2004-20213 A JP 7-325139 A Japanese Patent No. 4776918 International Publication No. 2013/047537 Pamphlet International Publication No. 2014/157661 Pamphlet

According to the magnetic field observation apparatus that performs the demodulation process by applying an alternating magnetic field as described in Patent Documents 4 and 5, when observing the direct magnetic field generated from the surface of the magnetic material sample, it is between the sample surface and the probe. It is possible to eliminate the influence of the surface force, which is a strong attractive force, and to increase the spatial resolution. This is because the magnetic force acting on the probe changes with time according to the change of the alternating magnetic field, while the surface force acting on the probe is not affected by the alternating magnetic field.

The magnetic field observation apparatus of Patent Document 4 and the magnetic profile measurement apparatus described in Patent Document 5 are based on the premise that a relatively weak DC magnetic field (for example, a surface magnetic field of a magnetic recording medium used in a magnetic storage device) is measured. In these conventional alternating magnetic force microscopes, it is common to use a soft magnetic material with easy magnetization reversal among the ferromagnetic materials for the probe. However, when a magnetic material sample that generates a strong magnetic field (for example, 10 kOe or more) like a permanent magnet is to be observed with a magnetic force microscope using these conventional magnetic force microscope probes, the following (1) Problems (3) arise.

(1) Since the magnetic material of the probe has a large magnetic moment, the probe is adsorbed on the sample surface by a strong DC magnetic field generated from the magnetic sample, making measurement itself difficult. Since there is a limit to the thinness with which the magnetic film of the probe can be formed with good quality, it is difficult to avoid this problem by adjusting the magnetic film thickness of the probe.

(2) The probe magnetization is saturated by the strong surface magnetic field from the sample, and the magnetic force acting on the probe does not fluctuate due to the external AC magnetic field, so no frequency modulation occurs in the probe vibration. Gradient measurement becomes difficult.

(3) Since the signal intensity is too strong, the quantization error of the A / D converter cannot be ignored, and a large error (for example, a phase error of about 20 to 30 °) is generated. As one countermeasure against this problem, it is conceivable to lower the Q value of the probe by performing measurement in the atmosphere, but this greatly reduces the spatial resolution. As another countermeasure, it is conceivable to dispose the probe at a position farther from the sample, but with such an arrangement, the spatial resolution is greatly reduced.

The first problem of the present invention is to observe a magnetic field gradient with a high spatial resolution using a magnetic force microscope even for a magnetic sample that generates a strong (for example, 10 kOe or more) DC magnetic field as represented by a permanent magnet. It is to provide a probe for a magnetic force microscope that makes it possible.

A second problem of the present invention is a magnetic field observation apparatus capable of observing a magnetic field with high spatial resolution in the vicinity of the surface of a magnetic sample that generates a strong DC magnetic field, such as a permanent magnet. And a magnetic field observation method.

Also, the conventional alternating magnetic force microscope measures the magnetic field gradient on the surface of the observation sample, and cannot measure the magnetic field itself. On the other hand, the present inventors have developed a magnetic field measuring method and a magnetic field value measuring apparatus capable of measuring an absolute value including positive and negative of a DC magnetic field generated from a magnetic material sample, and have applied for a patent (Japanese Patent Application No. 2013-2013). No. 069762 and PCT / JP2014 / 59276. Published as Patent Document 6). This device excites a magnetic probe having the property that the magnetization is zero when the external magnetic field is zero in a state where a DC magnetic field generated from the observation sample is applied, and is not zero in the vibration direction of the probe (large ) The excitation vibration of the probe is frequency-modulated by applying an AC external magnetic field having a change rate and a frequency different from the mechanical vibration frequency of the probe. Then, by canceling the DC magnetic field from the observation sample applied to the tip of the probe by applying a DC external magnetic field, the frequency modulation of the probe vibration is weakened, and the direct current when the magnitude of the frequency modulation becomes a minimum near zero Measure the external magnetic field. A DC magnetic field having a polarity opposite to the DC external magnetic field at this time is a DC magnetic field generated from the observation sample. The probe used in this measuring method and measuring apparatus has a magnetic characteristic in which the magnetization is zero when the magnetic field is zero in the range used for measurement, and the strength of magnetization is proportional to the magnitude of the magnetic field. Is preferred.

A third subject of the present invention is a magnetic force microscope that makes it possible to measure the absolute value including the positive and negative of a DC magnetic field generated from a magnetic sample, even for a magnetic sample that generates such a strong DC magnetic field. Is to provide a probe.

The present invention includes the following forms [1] to [22].
[1] comprising at least one magnetic material;
Magnetization does not saturate when a magnetic field is applied at room temperature, more specifically over a temperature range of at least 10-30 ° C.,
(A) the magnetic material is a solid solution of one or more ferromagnetic elements and one or more nonmagnetic elements;
(B) the magnetic material is an amorphous magnetic material containing one or more ferromagnetic elements and one or more nonmagnetic elements; or (c) the magnetic material is one or more ferromagnetic particles. And a magnetic material having a structure in which ferromagnetic particles are dispersed and supported in the nonmagnetic material.

In this specification, “magnetization is not saturated (no magnetic saturation)” for a magnetic probe is determined based on the fact that magnetization is not saturated when an external magnetic field of 20 kOe is applied.

In this specification, a certain material being “superparamagnetic material” or “superparamagnetic material” means that the material exhibits superparamagnetism. A material “shows superparamagnetism” means that particles of a ferromagnetic material having spontaneous magnetization contained in the material (in the present invention, “ferromagnetic material” includes a ferrimagnetic material) are adjacent to each other. Due to the weak magnetic interaction with the particles and the small particle size, the magnetization direction of each particle changes randomly under the influence of thermal energy, and the magnetization of the entire material without applying a magnetic field Means an average of zero.

[2] The magnetic force microscope according to [1], which has no remanent magnetization at room temperature under a condition where no magnetic field is applied, more specifically over a temperature range of at least 10 to 30 ° C. Probe.

[3] In the above [1] or [2], the initial magnetic susceptibility of the magnetic material is 3 × 10 ⁻⁸ H / m or more at room temperature, more specifically over a temperature range of at least 10 to 30 ° C. The magnetic force microscope probe described.

[4] The requirement (a) or (b) is satisfied, and the ferromagnetic element is one or more ferromagnetic elements selected from the group consisting of Ni, Fe, and Co, and the nonmagnetic element is One or more nonmagnetic elements selected from the group consisting of Ti, V, Cr, Mn, Cu, Zn, Zr, Nb, Mo, Ta, W, B, Al, C, O, N, and Si; The probe for a magnetic force microscope according to any one of [1] to [3], which preferably contains at least one element selected from Cr, Mn, and Mo as a nonmagnetic element.

[5] The probe for a magnetic force microscope according to any one of [1] to [4], which satisfies the requirement (a) or (b), and wherein the magnetic material exhibits paramagnetism or superparamagnetism.

[6] The requirement (c) is satisfied, and the content of the ferromagnetic particles is 10 to 45% by volume, preferably 15 to 40% by volume, based on the total amount of the magnetic material. The magnetic force microscope probe according to any one of [1] to [3], wherein the amount is 55 to 90% by volume, preferably 60 to 85% by volume.

[7] [1] to [3] and [6] satisfying the above-mentioned requirement (c), and the average value of the spherical equivalent diameter of the ferromagnetic particles by the image analysis method is 30 nm or less, preferably 5 to 10 nm. A probe for a magnetic force microscope according to any one of the above.

Here, the spherical equivalent diameter by the image analysis method of the ferromagnetic particles means that when the surface of the magnetic material is observed at a magnification of 100,000 to 200,000 times by secondary electron detection using a scanning electron microscope (SEM). Furthermore, the diameter of a circle having an area equal to the area occupied by ferromagnetic particles in the SEM image is meant. And the average value shall mean the value which took the arithmetic average of the said spherical conversion diameter about 100 or more ferromagnetic particles of the same magnetic material sample.

[8] Satisfying the requirement (c) above, the ferromagnetic particles are particles of one or more ferromagnetic elements selected from the group consisting of Ni, Fe, and Co, and the nonmagnetic material is Au, Ag , Cu, silicon dioxide, titanium oxide, tungsten oxide, chromium oxide, cobalt oxide, tantalum oxide, boron oxide, magnesium oxide, cerium oxide, yttrium oxide, nickel oxide, aluminum oxide, ruthenium oxide, rare earth element oxide, and carbon The probe for a magnetic force microscope according to any one of [1] to [3], [6] and [7], which is at least one nonmagnetic material selected from the group consisting of:

[9] The probe for a magnetic force microscope according to any one of [1] to [3] and [6] to [8], which satisfies the requirement (c) and the magnetic material exhibits superparamagnetism.

[10] The conditions of [1] to [3] and [6] to [9], which satisfy the requirement (c) above and the magnetic susceptibility has substantially no temperature dependence in the temperature range of 25 to 200 ° C. The magnetic force microscope probe according to any one of the above.

Here, the magnetic susceptibility “has substantially no temperature dependence in the temperature range of 25 to 200 ° C.” means that each of the five temperature conditions of 25 ° C., 50 ° C., 100 ° C., 150 ° C., and 200 ° C. When the initial magnetic susceptibility of the magnetic material is measured, it means that the variation of the five measured values is within ± 10% with respect to the arithmetic average value of the five measured values.

[11] The above-mentioned requirement (c) is satisfied, and the initial susceptibility of the magnetic material is 2 × 10 ⁻⁷ H / m or more, specifically over a temperature range of at least 10 to 30 ° C. at room temperature. The probe for a magnetic force microscope according to any one of [1] to [3] and [6] to [10], which is preferably 1 × 10 ⁻⁶ H / m or more.

[12] The magnetic material according to any one of [1] to [11], comprising a core member made of one or more kinds of nonmagnetic materials and a coating of the magnetic material that covers at least a part of the surface of the core member. Probe for force microscope.

[13] A magnetic field observation apparatus for observing a direct-current magnetic field leaking from a magnetic sample, having a magnetic probe at one end that has no magnetic saturation and generates a magnetic moment in the applied magnetic field direction; excites the cantilever An AC magnetic field generator for applying frequency modulation to the excitation vibration of the cantilever by applying an AC magnetic field of a magnitude that does not reverse the magnetization of the magnetic material to the probe and periodically changing the magnetization of the probe. A vibration sensor for detecting the vibration of the probe; a demodulator for demodulating a signal corresponding to an AC component of the magnetic force generated between the probe and the observation sample from the detection signal of the vibration sensor; A demodulated signal processing device that obtains DC magnetic field information from the demodulated signal and the voltage signal of the AC magnetic field generator; and a scanning mechanism that causes the probe to scan the scanning region on the surface of the magnetic sample. For example, the magnetic probe is [1] to [12] magnetic force, characterized in that a microscope probe, a strong magnetic field generated magnetic field observation apparatus sample according to any one of.

In this specification, “no magnetic saturation” in the magnetic probe is determined based on the fact that magnetization is not saturated when an external magnetic field of 20 kOe is applied.

[14] The demodulator
(A) The frequency of the detection signal of the vibration sensor is demodulated, or
(B) Measure the intensity of the sideband spectrum included in the detection signal of the vibration sensor,
[13] The magnetic field observation apparatus according to [13].

[15] The demodulated signal processing apparatus includes:
(X) measuring the amplitude of the demodulated signal obtained from the demodulator and the phase difference between the demodulated signal and the current signal or voltage signal of the AC magnetic field generator;
(Y) measuring the in-phase component and the quadrature component of the demodulated signal obtained from the demodulator with respect to the current signal of the AC magnetic field generator;
The magnetic field observation apparatus according to [13] or [14].

[16] The magnetic field observation apparatus according to any one of [13] to [15], wherein the AC magnetic field generation mechanism applies an AC magnetic field in the same direction as the direction of the component to be measured of the DC magnetic field.

[17] The magnetic field observation apparatus according to any one of [13] to [16], wherein the magnetic sample is a permanent magnet.

[18] The image display device according to [13] to [17], further including an image display device that displays a magnetic field distribution image based on DC magnetic field information at each coordinate of the scanning region obtained by scanning the scanning region with the scanning mechanism. The magnetic field observation apparatus according to any one of the above.

[19] A magnetic field observation method for observing a DC magnetic field leaking from a magnetic material sample, the method comprising exciting a cantilever having a magnetic probe that generates no magnetic saturation in the applied magnetic field direction at one end without magnetic saturation. Applying an alternating magnetic field of a magnitude that does not reverse the magnetization of the magnetic sample to the probe, and periodically modulating the magnetization of the probe to frequency-modulate the excitation vibration of the cantilever; and detecting the probe vibration And a step of demodulating a signal corresponding to an alternating current component of the magnetic force generated between the probe and the observation sample from the detection signal; and a DC magnetic field from the demodulated signal and the voltage signal of the alternating magnetic field generator. A step of obtaining information; and a step of causing the probe to scan a scanning region on the surface of the magnetic material sample, wherein the magnetic probe is the probe for a magnetic force microscope according to any one of [1] to [12] Features that are To, strong magnetic field generated magnetic field observation method of the specimen.

[20] The magnetic field observation method according to [19], wherein an alternating magnetic field is applied in the same direction as the direction of the component to be measured of the direct magnetic field.

[21] The magnetic field observation method according to [19] or [20], wherein the magnetic sample is a permanent magnet.

[20] The method further includes a step of displaying, on the image display device, a magnetic field distribution image based on DC magnetic field information at each coordinate of the scanning region obtained by scanning the scanning region with the scanning mechanism. ] Magnetic field observation method in any one of.

By using the magnetic force microscope probe of the present invention for a magnetic force microscope, for example, a magnetic sample that generates a strong DC magnetic field represented by a permanent magnet can be observed with a magnetic force microscope with high spatial resolution. It becomes possible to do.

According to the magnetic field observation apparatus and magnetic field observation method of the present invention, it is possible to observe a magnetic field with high spatial resolution near the surface of a magnetic sample that generates a strong DC magnetic field, such as a permanent magnet. is there. Also, the polarity of the magnetic pole on the surface of the magnetic material sample can be detected.

It is a figure which illustrates typically the composition of the probe for magnetic force microscopes concerning one embodiment of the present invention. FIG. 2 is an AA arrow view of FIG. 1. It is a flowchart explaining the method to manufacture the probe for magnetic force microscopes concerning one Embodiment of this invention. It is a figure which illustrates typically the structure of the sputtering device used for film-forming of a magnetic film. It is a figure which illustrates typically the composition of the magnetic field observation device concerning one embodiment of the present invention. It is a figure for demonstrating the measurement principle by the magnetic field observation apparatus of this invention. 2 is a graph showing the results of magnetic property evaluation of an Fe—Mn solid solution paramagnetic thin film formed in Example 1. FIG. 6 is a graph group showing the results of magnetic property evaluation of an Fe—Mo—B amorphous paramagnetic thin film formed in Example 2. FIG. 10 is a graph showing the results of initial susceptibility evaluation of a Co—Ag granular superparamagnetic thin film formed in Example 3. Among the Co—Ag granular superparamagnetic thin films formed in Example 3, the magnetization curve of the Ag ₇₉ Co ₂₁ thin film (deposition rate 0.80 nm / sec) and the Ag ₈₅ Co ₁₅ thin film (deposition rate 0) .20 nm / sec) is compared with the magnetization curve. Of the Co—Ag granular superparamagnetic thin film formed in Example 3, the temperature dependence of the initial magnetic susceptibility of the Ag ₇₉ Co ₂₁ thin film (deposition rate 0.80 nm / sec) and the Ag ₈₃ Co ₁₇ thin film It is a graph group which compares the temperature dependence of the initial magnetic susceptibility of (film formation rate 0.54 nm / sec). It is a figure which shows the observation result in the surface vicinity of Example 4 in Example 4. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawing, some symbols may be omitted. In the present specification, “A to B” for numerical values A and B means “A or more and B or less” unless otherwise specified. In the notation, when the unit of the numerical value A is omitted, the unit attached to the numerical value B is applied as the unit of the numerical value A. In addition, the form shown below is an illustration of this invention and this invention is not limited to these forms.

<1. Magnetic Force Microscope Probe>
FIG. 1 is a diagram schematically illustrating a magnetic force microscope probe 100 (hereinafter sometimes abbreviated as “probe 100”) according to an embodiment of the present invention, and FIG. FIG. 2 is an AA arrow view of FIG. 1. As shown in FIGS. 1 and 2, a magnetic force microscope probe 100 includes a triangular pyramid-shaped core member 10 made of a non-magnetic material, and a coating of a magnetic material that covers at least a part of the surface of the core member 10. 30 (hereinafter sometimes abbreviated as “magnetic coating 30”). The magnetic force microscope probe 100 is erected at one end of the cantilever 20 by fixing the bottom surface of the triangular pyramid-shaped core member to one end of the cantilever 20. As shown in FIG. 1, the magnetic material coating 30 may cover not only the surface of the core member 10 but also the surface of the cantilever 20.

The probe 100 is provided with at least one magnetic material by covering the surface of the core member 10 with the magnetic coating 30. The probe 100 is characterized in that the magnetization does not saturate when a magnetic field is applied at room temperature, more specifically over a temperature range of at least 10 to 30 ° C. Therefore, by using the probe 100 for an alternating magnetic force microscope, even when a strong magnetic field generating sample such as a permanent magnet is observed, the saturation of the probe magnetization due to the strong surface magnetic field from the sample does not occur. Frequency modulation can be generated in the probe vibration by applying a magnetic field. Therefore, it is possible to observe the magnetic field with high spatial resolution using an alternating magnetic force microscope.

Preferably, the probe 100 does not have magnetization at room temperature, more specifically, at least in the temperature range of 10 to 30 ° C. under a condition where no magnetic field is applied, regardless of whether the probe 100 is demagnetized or magnetized. According to the probe 100 having no remanent magnetization (and hence no hysteresis) under a condition in which no magnetic field is applied, high-precision measurement is possible when measuring a DC magnetic field gradient using an alternating magnetic force microscope. Become.

(Core member 10)
The core member 10 is made of a non-magnetic material and is a member that determines the general shape of the probe 100 and plays a role of holding the magnetic coating 30 on the surface. One end portion of the core member 10 is erected on one end portion of the cantilever 20, and the other end portion of the core member 10 is shaped so as to point toward the tip. As the nonmagnetic material constituting the core member 10, a nonmagnetic material having a strength necessary for maintaining the shape of the probe 100 can be used without particular limitation, such as Si, Si—N, Si—O, and the like. Can be preferably used.
In the probe 100 shown in FIGS. 1 and 2, the core member 10 has a triangular pyramid shape, but the shape of the core member 10 is not limited to the triangular pyramid shape. The shape can be appropriately selected as long as the spatial resolution and the necessary intensity required for magnetic field observation with a magnetic force microscope can be ensured. However, from the viewpoint of increasing the spatial resolution of magnetic field observation, it is preferable that the shape has a sharp tip portion, and the end portion on the side fixed to the cantilever 20 has some degree to facilitate fixing to the cantilever 20. It is preferable to have a size of Considering such circumstances, a pyramid shape such as a triangular pyramid shape, a quadrangular pyramid shape, or a conical shape can be preferably employed.

(Magnetic coating 30)
The magnetic material constituting the magnetic coating 30 can be one or more magnetic materials selected from the group consisting of paramagnetic materials and superparamagnetic materials. Since the magnetic moment of magnetic materials other than these ferromagnetic materials is much smaller than that of ferromagnetic materials, the magnetic film 30 is composed of these magnetic materials, so that a magnetic field generating sample such as a permanent magnet can be obtained using a magnetic force microscope. Even when the magnetic field is observed, the probe is detected by the magnetic force acting on the probe 100 due to the magnetic interaction between the magnetic moment induced in the probe 100 by the magnetic field from the magnetic sample and the magnetic moment of the magnetic sample. It is possible to prevent the needle 100 from being magnetically attracted to the magnetic sample. The film thickness of the magnetic coating 30 is determined by the measurement sensitivity in the magnetic force microscope (the sensitivity increases as the magnetic coating 30 is thicker) and the spatial resolution (the tip of the probe 100 becomes duller as the magnetic coating 30 is thicker). Can be determined as appropriate in consideration of a tradeoff with The initial magnetic susceptibility of the magnetic material constituting the magnetic coating 30 is preferably 3 × 10 ⁻⁸ H / m or more at room temperature, more specifically over a temperature range of at least 10 to 30 ° C.

Paramagnetic materials show the greatest magnetic susceptibility near the Curie temperature (Hopkinson effect). Therefore, as a paramagnetic material that can be preferably used as the magnetic material constituting the magnetic coating 30, it is possible to increase the magnetic susceptibility by adjusting the Curie temperature of the paramagnetic material and increase the measurement sensitivity of the magnetic force microscope. In this respect, a magnetic material containing one or more ferromagnetic elements and one or more nonmagnetic elements can be preferably used. Specifically, (a) one or more kinds of ferromagnetic elements and one or more kinds of nonmagnetic elements formed a solid solution (hereinafter sometimes referred to as “solid solution type paramagnetic material”), and ( b) A material in which one or more kinds of ferromagnetic elements and one or more kinds of nonmagnetic elements form an amorphous structure (hereinafter sometimes referred to as “amorphous paramagnetic material”) can be preferably used. In these multicomponent paramagnetic materials, the ferromagnetic element is one or more ferromagnetic elements selected from the group consisting of Ni, Fe, and Co, and the nonmagnetic elements are Ti, V, Cr, One or more nonmagnetic elements selected from the group consisting of Mn, Cu, Zn, Zr, Nb, Mo, Ta, W, B, Al, C, O, N, and Si are preferable. From the viewpoint of lowering the Curie temperature with a small amount of nonmagnetic element, it is more preferable to include one or more elements selected from Cr, Mn, and Mo as the nonmagnetic element.

The (a) solid solution type paramagnetic material has a composition in which the total content of ferromagnetic elements is 50 to 70 atomic% and the total content of nonmagnetic elements is 30 to 50 atomic% with respect to the total amount of the solid solution type paramagnetic material. It is preferable to have.

The amorphous paramagnetic material (b) has a total content of ferromagnetic elements of 70 to 90 atomic% and a total content of nonmagnetic elements of 10 to 30 atoms with respect to the total amount of the amorphous paramagnetic material. % Of the composition.

Specific examples of the (a) solid solution type paramagnetic material include Ni—Cr solid solution (for example, Ni ₉₃ Cr ₇ (initial magnetic susceptibility 4.7 × 10 ⁻⁸ H / m at 25 ° C.)), Fe—Cr solid solution ( For example, Fe ₅₉ Cr ₄₁ (initial magnetic susceptibility 6.0 × 10 ⁻⁸ H / m at 25 ° C.), Fe—Mn solid solution (eg Fe ₆₇ Mn ₃₃ (initial magnetic susceptibility 1.2 × 10 ⁻⁷ H at 25 ° C.) / M)) etc. can be mentioned preferably.

Specific examples of the (b) amorphous paramagnetic material include Fe—Mo—B amorphous materials (for example, Fe ₈₆ Mo _7.5 B _6.5 (initial magnetic susceptibility of 1.4 × 10 5 at 25 ° C.). ^-7 H / m)) and the like can be preferably mentioned.

In producing the magnetic coating 30 with these multicomponent paramagnetic materials, for example, a method of depositing each component on the surface of the core member 10 by simultaneous sputtering can be preferably employed. At that time, the composition of the magnetic coating 30 deposited on the surface of the core member 10 can be adjusted by the amount of electric power applied to the sputtering target of each component and the amount of the thin film material sheet attached to the sputtering target.

The magnetic material that can be used for the magnetic coating 30 and exhibits superparamagnetism includes (c) one or more types of ferromagnetic particles and one or more types of nonmagnetic materials, and the ferromagnetic particles are nonmagnetic. A magnetic material having a structure dispersed and supported in the material (hereinafter sometimes referred to as “granular superparamagnetic material”) can be preferably exemplified. In granular superparamagnetic materials, fine ferromagnetic particles are dispersed in a non-magnetic matrix and exist in a magnetically isolated state, and the magnetic energy of the ferromagnetic particles is below a certain threshold with respect to thermal energy. As a result, the magnetic moment of the ferromagnetic particles changes its direction at random due to the influence of heat, so that superparamagnetism appears.

When a granular superparamagnetic material is used for the magnetic coating 30, the content of the ferromagnetic particles is 10 to 45% by volume and the content of the nonmagnetic material is 55 to 90% by volume with respect to the total amount of the magnetic material. Is preferred. By making the content of the ferromagnetic particles within the above range, contact between the ferromagnetic particles can be suppressed, so that it is easy to realize a magnetically isolated state of the ferromagnetic particles. From the same viewpoint, the content of the ferromagnetic particles is more preferably 15 to 40% by volume, and the content of the nonmagnetic material is more preferably 60 to 85% by volume.

From the viewpoint of reducing the magnetic energy of the ferromagnetic particles and facilitating the randomization of the magnetic moment by the thermal energy, the particle size of the ferromagnetic material particles in the granular superparamagnetic material is the sphere equivalent diameter by image analysis. The average value is preferably 30 nm or less, and more preferably 5 to 10 nm. The particle size of the ferromagnetic material has a critical particle size unique to the material. When the particle size of the ferromagnetic material exceeds this critical particle size, the ferromagnetic material particle changes from the superparamagnetic state to the ferromagnetic state and exhibits magnetic hysteresis. Therefore, the size of the ferromagnetic material particles is preferably set to be equal to or smaller than the critical particle size of the material. For example, when cobalt (Co) having a face-centered cubic structure (fcc) is used as the ferromagnetic material, the particle size of the cobalt particles is preferably 30 nm or less, and more preferably 10 nm or less. Here, the sphere equivalent diameter by the image analysis method of the ferromagnetic particles means that when the surface of the magnetic material is observed at a magnification of 100,000 to 200,000 by secondary electron detection using a scanning electron microscope (SEM). And the diameter of a circle having an area equal to the area occupied by ferromagnetic particles in the SEM image. And the average value shall mean the value which took the arithmetic average of the said spherical conversion diameter about 100 or more ferromagnetic particles of the same magnetic material sample.

(C) Examples of the constituent material of the granular superparamagnetic material include a combination of a non-solid solution metal composed of a ferromagnetic metal and a nonmagnetic metal, and a combination of a ferromagnetic metal and a nonmagnetic nonmetallic material.

In the granular superparamagnetic material, as the ferromagnetic particles, particles of one or more ferromagnetic elements selected from the group consisting of Ni, Fe, and Co can be preferably used, and as the nonmagnetic material, Au, Ag, From Cu, silicon dioxide, titanium oxide, tungsten oxide, chromium oxide, cobalt oxide, tantalum oxide, boron oxide, magnesium oxide, cerium oxide, yttrium oxide, nickel oxide, aluminum oxide, ruthenium oxide, rare earth element oxide, and carbon One or more non-magnetic materials selected from the group can be preferably used. As the rare earth element oxide, for example, gadolinium oxide, terbium oxide and the like can be preferably employed.

As a granular type superparamagnetic material by a combination of non-solid solution metals, for example, particles of Co, which is a ferromagnetic metal, are dispersed in a matrix of one or more nonmagnetic metals selected from the group consisting of Cu, Ag, and Au. The material can be mentioned.

Examples of superparamagnetic materials by combining ferromagnetic metals and nonmagnetic nonmetallic materials include, for example, silicon dioxide, titanium oxide, tungsten oxide, chromium oxide, cobalt oxide, tantalum oxide, boron oxide, magnesium oxide, cerium oxide, and yttrium oxide. Selected from the group consisting of Fe, Co, and Ni in a matrix of one or more nonmagnetic non-metallic materials selected from the group consisting of nickel oxide, aluminum oxide, ruthenium oxide, rare earth element oxide, and carbon A material in which particles of one or more kinds of ferromagnetic metals are dispersed can be given. As the rare earth element oxide, for example, gadolinium oxide, terbium oxide and the like can be preferably employed.

As will be described later, the film of the granular type superparamagnetic material is formed by, for example, forming a nonmagnetic material and a ferromagnetic material at a higher film deposition rate than usual (for example, 0.2 to 1.0 nm / sec in the case of Ag-Co). )) By co-sputtering. Since the material is rapidly cooled by increasing the deposition rate, the size of the dispersed ferromagnetic material particles can be reduced.

According to the granular type superparamagnetic material, it is possible to realize a high magnetic susceptibility that cannot be obtained with a paramagnetic material. For example, the initial magnetic susceptibility of a granular superparamagnetic material at room temperature is preferably 2 × 10 ⁻⁷ H / m or more, and can be 1 × 10 ⁻⁶ H / m or more. Therefore, according to the probe 100 using a granular superparamagnetic material for the magnetic coating 30, it is possible to increase the measurement sensitivity of the magnetic force microscope even with the same film thickness. Further, since the same level of measurement sensitivity can be obtained with a thinner film thickness, the tip of the probe 100 can be sharpened, and thus the spatial resolution of magnetic field measurement by a magnetic force microscope can be increased. .

Furthermore, according to the embodiment using a granular superparamagnetic material for the magnetic coating 30, it is possible to obtain the probe 100 with improved temperature stability of magnetic characteristics. For example, the probe 100 having no temperature dependency in the range of the magnetic susceptibility in the range from room temperature 25 ° C. to 200 ° C. may be used. For example, in the evaluation of the domain structure of a permanent magnet, it is important to measure the temperature change. Even if the temperature dependence of the magnetic domain structure of the permanent magnet is measured using a needle, the hard magnetic characteristics of the probe also change, and it is difficult to quantitatively evaluate the temperature dependence of the magnetic domain structure. The probe 100 using a granular superparamagnetic material for the magnetic coating 30 has improved temperature stability of magnetic characteristics such as initial magnetic susceptibility. Therefore, for example, the temperature of the magnetic sample is observed as in the observation of the magnetic domain structure of a permanent magnet. Even when the dependence is evaluated, it is possible to obtain a highly accurate evaluation result.

(Manufacture of magnetic force microscope probe 100)
A method for manufacturing the magnetic force microscope probe 100 will be described. In the following, a form of manufacturing the probe 100 in a form using a granular superparamagnetic material for the magnetic coating 30 will be mainly exemplified, but the present invention is not intended to be limited to the form.

FIG. 3 is a flowchart for explaining a manufacturing method S10 of the probe 100 (hereinafter sometimes simply referred to as “manufacturing method S10”). As shown in FIG. 3, the manufacturing method S <b> 10 includes a step S <b> 1 for preparing the core member 10 fixed to one end of the cantilever 20 (hereinafter sometimes simply referred to as “step S <b> 1”), and a core. Step S2 for forming the magnetic coating 30 on the exposed surface of the member 10 (hereinafter sometimes simply referred to as “Step S2”) is included in the above order.

(Process S1)
In step S1, a core member 10 made of Si, which is a nonmagnetic material, is prepared. The core member 10 is processed so as to have a shape desired for the probe 100. Specifically, the core member 10 can be manufactured, for example, by performing anisotropic etching on a Si single crystal wafer. The core member 10 is fixed to one end of the cantilever 20. The core member 10 can be fixed to the cantilever 20 by a known method. Thereafter, the core member 10 and the cantilever 20 are handled as a unit in a later process.
In addition, as Si which comprises the core member 10, in order to ensure electroconductivity, you may use Si doped with an impurity.

(Process S2)
Step S2 is a step of forming the magnetic coating 30 on the exposed surface of the core member 10 by simultaneous sputtering. FIG. 4 is a diagram illustrating the sputtering apparatus 200 used in step S2. The sputtering apparatus 200 has a sealed chamber 41 (a chamber for a magnetron sputtering apparatus, which may be abbreviated as “chamber 41” in the following). In the chamber 41, a rotation holding base 42 that is rotatably arranged through a rotation drive shaft 43 and rotatably holds the core member 10, and a ferromagnetic element target 44 (for example, a Co target. 44 ”and a non-magnetic element target 45 (for example, an Ag target. Hereinafter, it may be abbreviated as“ target 45 ”). Argon gas is supplied into the chamber 41 in a vacuumed state so that the core member 10 can be sputtered. The distance between each

target

44, 45 and the core member 10 can be changed from 70 mm to 120 mm.

The ferromagnetic element target 44 is connected to a DC power source for sputtering. The nonmagnetic element 45 is connected to a high frequency (for example, RF) power source for sputtering.

The frequency of the high frequency power source for the nonmagnetic element target 45 can be set to 13.56 MHz, for example. High power is applied to each

target

44 and 45 so that high-speed argon ions for sputtering are directed to each

target

44 and 45. The composition of the magnetic coating film 30 formed by sputtering can be adjusted by changing the power applied to each of the targets 44 and 45 (the diameter can be set to 75 mm, for example), for example (50 W to 250 W, etc.). It is like that.

The core member 10 integrated with the cantilever 20 is held by the rotation holding table 42. The rotation holding table 42 is rotated at a speed of, for example, 10 rpm during film formation. Further, the rotation holding table 42 can be moved up and down, and the distance between the rotation holding table 42 and the nonmagnetic element target 45 can be changed from 70 mm to 120 mm.

Next, the magnetic film 30 is formed by co-sputtering at room temperature. That is, both the ferromagnetic element target 44 and the nonmagnetic element target 45 are used as sputtering targets, and both elements are simultaneously formed by sputtering. In the magnetic film 30 to be deposited, the non-magnetic element (for example, Ag) does not dissolve in the ferromagnetic element (for example, Co), and the magnetic crystal grains of the ferromagnetic element (for example, Co) are non-magnetic elements (for example, Ag). ) Are dispersed and isolated in the non-magnetic grain boundary region (granular structure). The thickness of the magnetic coating 30 containing a nonmagnetic substance can be set to 10 to 100 nm, for example. For example, when a Co target is used as the ferromagnetic element target 44 and an Ag target is used as the nonmagnetic element target 45 and the film thickness is 100 nm, the time required for film formation is about 3 to 5 minutes. The magnetic force microscope probe 100 is manufactured through the steps S1 and S2.

In the above description regarding the method of manufacturing the probe 100 for the magnetic force microscope, the manufacturing process of the form in which the magnetic coating 30 is formed by co-sputtering a ferromagnetic element and a nonmagnetic element has been exemplified. The manufacturing method of the probe for use is not limited to this form.
For example, by alternately performing sputtering film formation of a nonmagnetic element (for example, Ag) and sputtering film formation of a ferromagnetic element (for example, Co), the magnetic film 30 containing a nonmagnetic material can be finally formed. It is. However, from the point that it is easy to realize a state where magnetic crystal grains of a ferromagnetic element (for example, Co) are dispersed and isolated in a nonmagnetic grain boundary region of a nonmagnetic element (for example, Ag). A form in which a magnetic film is formed by simultaneous sputtering as described above can be preferably employed.

<2. Magnetic field observation device>
FIG. 5 is a diagram schematically illustrating the magnetic field observation apparatus 1000 according to one embodiment of the present invention. The magnetic field observation apparatus 1000 is an apparatus that observes a DC magnetic field leaking from the magnetic sample 1.

As shown in FIG. 5, the magnetic field observation apparatus 1000 includes a probe 100, an exciter 200, an AC magnetic field generator 300, a vibration sensor 400, a demodulator 430, a demodulated signal processing device 440, the probe 100, and the magnetic material sample 1. Are provided with a scanning mechanism 500 that causes the probe 100 to scan the observation surface of the magnetic sample 1 and an image display device 600. Hereinafter, these components will be described.

(Magnetic material sample 1)
The magnetic material sample 1 that is a measurement target of the magnetic field observation apparatus 1000 is a sample that generates a strong DC magnetic field. A specific example of the magnetic material sample 1 is a permanent magnet.

(Probe 100)
The probe 100 is a magnetic probe that has no magnetic saturation and generates a magnetic moment in the direction of the applied magnetic field, and is provided at one end of the cantilever 11. The probe 100 is the magnetic force microscope probe 100 of the present invention described above. The probe 100 is affected by a direct-current magnetic field leaking from the magnetic sample 1 by being disposed on the magnetic sample 1. As will be described in detail later, the magnitude of the magnetization of the probe 100 is periodically changed in the direction of the AC magnetic field by the AC magnetic field generated from the AC magnetic field generator 300. At this time, the magnetic force acting on the probe 100 due to the magnetic interaction between the magnetization of the probe 100 and the DC magnetic field leaking from the magnetic sample 1 has an AC component. That is, the strength of the magnetic force acting on the probe 100 varies periodically. Therefore, the apparent spring constant of the cantilever 110 periodically varies, and as a result, the excitation vibration of the cantilever 110 (that is, the vibration of the probe 100) is frequency-modulated. The degree of periodic frequency modulation of the vibration of the probe 100 is measured by a demodulator 430 and a demodulated signal processing device 440 described later.

As described above, the probe 100 is a magnetic probe that has no magnetic saturation and generates a magnetic moment in the applied magnetic field direction. When a ferromagnetic or ferrimagnetic probe with magnetic saturation is used, the magnetization of the probe is saturated by the strong DC magnetic field leaking from the magnetic sample 1, and an AC magnetic field is applied. However, since the magnetization of the probe cannot be changed, frequency modulation cannot be caused in the excitation vibration of the cantilever.

As long as a magnetic material that does not have magnetic saturation and generates a magnetic moment in the direction of the applied magnetic field is included in the probe 100 and the problem that measurement cannot be performed due to the probe 100 being adsorbed to the magnetic sample 1 does not occur. The probe may contain a ferromagnet (ie, a material with magnetic saturation). Even if the magnetization of the ferromagnet is saturated by the DC magnetic field from the magnetic sample 1, the magnetization of the magnetic material without magnetic saturation can be changed by applying an AC magnetic field. It can be changed by applying. In the case of a probe containing a ferromagnetic material in the magnetic film, the residual magnetization is not zero but has hysteresis, but as long as a strong DC magnetic field such as a permanent magnet is observed, the magnetization of the entire probe is hysteresis. It fluctuates in a reversible region outside the region. Therefore, as long as the probe 100 is not attracted to the magnetic material sample 1 and the measurement itself is not disabled, the probe including the ferromagnetic material in addition to the magnetic material that does not have magnetization saturation and generates a magnetic moment in the direction of the applied magnetic field. It can be used in the invention.
However, from the viewpoint of measurement accuracy, the probe 100 preferably has no magnetic hysteresis.

As the magnetic material that has no magnetic saturation and generates a magnetic moment in the direction of the applied magnetic field, it is preferable to use a paramagnetic or superparamagnetic material, and to use a superparamagnetic material (superparamagnetic material). Is particularly preferred. Superparamagnetic materials exhibit a high magnetic susceptibility compared to paramagnetic materials, and are advantageous for magnetic field detection with high sensitivity.

The film thickness of the magnetic material in the probe 100 is not particularly limited, and can be appropriately determined in consideration of the trade-off between magnetic field measurement sensitivity and spatial resolution, and can be, for example, 10 to 100 nm.

As a paramagnetic material usable for the probe 100, a multi-component paramagnetic material containing one or more ferromagnetic elements and one or more nonmagnetic elements can be preferably exemplified. Paramagnetic materials exhibit the highest magnetic susceptibility near the Curie temperature (Hopkinson effect). Therefore, according to the multi-component paramagnetic material, the magnetic susceptibility at the measurement temperature can be adjusted by changing the composition and adjusting the Curie temperature. It is possible to increase the measurement sensitivity of the magnetic force microscope. Specifically, the (a) solid solution type paramagnetic material and the (b) amorphous type paramagnetic material can be preferably used as the multi-component paramagnetic material.

As the superparamagnetic material that can be used for the probe 100, the above-mentioned (c) granular superparamagnetic material (sufficiently small particles of a ferromagnetic material are dispersed in a nonmagnetic matrix, and the ferromagnetic material particles are 10 to 45 in total. Examples thereof include materials having a structure occupying volume%, preferably 15 to 40 volume%. Ferromagnetic material particles occupy 10 to 45% by volume of the whole, so percolation occurs (in the sphere approximation model, when two kinds of spheres are mixed, the same kind of spheres are not in contact with each other). Strong magnetic interaction (exchange interaction) between particles can be suppressed. When the size of the ferromagnetic material particle is reduced, the magnetization direction of the particle is randomized by thermal energy, and the magnetization of the individual particles cancels out in the absence of a magnetic field. Transition to magnetism. Since the magnetization is zero under no magnetic field, the residual magnetization and the coercive force are also zero at the same time. When a magnetic field is applied to a superparamagnetic material, magnetization occurs only in the direction of the magnetic field, and magnetization in the direction perpendicular to the magnetic field cancels between individual particles, so the superparamagnetic material does not have a magnetization component perpendicular to the direction in which the magnetic field is applied. .

Superparamagnetic materials transition from superparamagnetism to ferromagnetism as the temperature drops, and the transition temperature is called the blocking temperature. When a superparamagnetic material is used for the probe, the temperature of the probe in use is kept above the blocking temperature.

(Exciter 200)
The probe 100 is provided near one end (free end) of the cantilever 110, and the other end (fixed end) of the cantilever 110 is fixed. The probe 100 can be excited by exciting the cantilever 110 with the exciter 200.

As long as the probe 100 can be excited, the configuration of the exciter 200 is not particularly limited. The exciter 200 can be configured by, for example, an excitation actuator (for example, a piezo element) attached near the fixed end of the cantilever 110 and an AC voltage power source connected to the excitation actuator. The frequency at which the exciter 200 excites the cantilever 110 is not particularly limited as long as excitation is possible, but normally a frequency near the resonance frequency of the cantilever 110 is preferably adopted as the excitation frequency.

(AC magnetic field generator 300)
The AC magnetic field generator 300 is an apparatus that applies an AC magnetic field having a magnitude that does not cause magnetization reversal of the magnetic sample 1 to the probe 100. For example, as shown in FIG. 5, such an alternating magnetic field generation mechanism 300 is arranged immediately below the magnetic material sample 1, and a magnetic core 330 around which the coil 320 is wound, and an alternating current that supplies an alternating current to the coil 320. It can be constituted by a current power source 310. The coil 320 and the magnetic core 330 constitute an AC electromagnet. When an AC current is supplied from the AC current power source 310 to the coil 320, an AC magnetic field in a direction perpendicular to the sample surface is applied to the magnetic sample 1 and the probe 100. Applied.

It is preferable that the AC magnetic field generated from the AC magnetic field generator 300 has a small spatial change. Specifically, the DC component of the magnetization at the tip of the probe 100 (that is, the magnetization due to the DC magnetic field leaking from the magnetic sample 1) and the spatial change gradient of the AC magnetic field applied from the AC magnetic field generator 300 to the probe 100. Is the space between the AC component of the magnetization at the tip of the probe 100 (that is, the magnetization fluctuation due to the AC magnetic field applied from the AC magnetic field generator 300) and the DC magnetic field applied from the magnetic sample 1 to the probe 100. It is preferably smaller than the product of the change gradient. In order to reduce the spatial change gradient of the alternating magnetic field, it is conceivable to apply an alternating magnetic field having a uniform size to the measurement space between the magnetic sample 1 and the probe 100.

Further, the AC magnetic field generator 300 is used in the case of measuring a DC magnetic field in the same direction as the component to be measured of the DC magnetic field leaking from the magnetic sample 1 (for example, a direction perpendicular to the observation surface of the magnetic sample 1). Is preferably applied in the direction perpendicular to the observation plane). The reason is that in the magnetic force microscope of the present invention, a magnetic field component (projection component in the magnetization direction of the probe) generated in the direction of application of the alternating magnetic field and parallel to the magnetization direction of the probe is detected. .

Note that the frequency of the AC magnetic field generated from the AC magnetic field generator 300 is not particularly limited as long as the frequency modulation of the vibration of the probe 100 can be detected, and may be, for example, 10 Hz to 1 kHz. For example, when the exciter 200 excites the cantilever 110 at the resonance frequency or a frequency close to the resonance frequency, the sideband frequency generated by frequency modulation of the excitation vibration can obtain a necessary gain in the resonance curve. A frequency that falls within the range can be appropriately selected.

The intensity of the AC magnetic field applied to the probe 100 by the AC magnetic field generator 300 is appropriately adjusted within a range where the probe 100 is not attracted to the magnetic sample 1 and a desired magnetic field measurement sensitivity can be obtained. be able to.

The installation position of the elements constituting the AC magnetic field generation mechanism 300 is not particularly limited. For example, in the magnetic field observation apparatus 1000 shown in FIG. 5, an AC electromagnet composed of a magnetic core 330 and a coil 320 is arranged immediately below the magnetic sample 1. In order to incorporate the AC magnetic field generation mechanism 300 into a conventional general-purpose MFM in which the space around the probe 100 is narrow, it is considered that an AC electromagnet or the like that generates an AC magnetic field is installed under the MFM sample mounting table. It is done. Alternatively, the AC magnetic field generation mechanism 300 can be installed so that the space around the probe 100 can be widened and an AC magnetic field can be applied to the probe 100 from a position closer to the probe 100 than the magnetic sample 1. It is.

(Vibration sensor 400, demodulator 430, demodulated signal processing device 440)
Due to the magnetic interaction between the magnetization of the probe 100 and the DC magnetic field from the magnetic sample 1, the probe 100 receives a magnetic force whose intensity periodically varies. This magnetic force whose intensity periodically changes causes the apparent spring constant of the cantilever 110 to periodically change. In this way, the apparent spring constant of the cantilever 110 periodically varies, so that the vibration frequency of the probe 100 varies periodically. The vibration sensor 400, demodulator 430, and demodulated signal processing device 440 can extract DC magnetic field information from the magnetic sample 1 at the position of the probe 100 from the vibration of the probe 100 that has been frequency-modulated.

(Vibration sensor 400)
In the magnetic field observation apparatus 1000, the vibration sensor 400 includes a light source 410 that irradiates laser light on the free end of the cantilever 110 and an optical displacement sensor 420 that detects the laser light reflected by the cantilever 110. Yes. By detecting the laser beam emitted from the light source 410 and reflected by the free end of the cantilever 110 with the optical displacement sensor 420, the displacement of the probe 100 can be extracted as an output. An output from the optical displacement sensor 420 detected by the scanning mechanism 600 described later while scanning the observation surface of the magnetic sample 1 with the probe 100 is input to the demodulator 430.

(Demodulator 430)
The detection signal of the vibration sensor 400 is a vibration in which the excitation vibration of the cantilever 110 is frequency-modulated by the AC component of the magnetic force generated between the probe 100 and the magnetic sample 1. The demodulator 430 demodulates a signal corresponding to the alternating current component of the magnetic force generated between the probe 100 and the magnetic sample 1 from the detection signal of the vibration sensor 400. In the magnetic field observation apparatus 1000 of FIG. 5, the demodulator 430 is an FM demodulator that frequency-demodulates the detection signal of the vibration sensor 400. As the demodulator 430, a circuit known as an FM demodulator, such as a PLL (Phase Locked Loop) circuit, can be employed without any particular limitation. As the demodulator 430, a demodulator that measures the intensity of the sideband spectrum included in the detection signal of the vibration sensor 400 can be adopted. For example, a spectrum analyzer is used as the demodulator. Can be configured. The signal demodulated by the demodulator 430 is input to the demodulated signal processing device 440.

(Demodulated signal processing device 440)
The demodulated signal processing device 440 extracts DC magnetic field information from the demodulated signal input from the demodulator 430 and the voltage signal from the AC magnetic field generator 300. In the magnetic field observation apparatus 1000 of FIG. 5, the demodulated signal processing apparatus 440 is configured by a lock-in amplifier. The demodulated signal processing device 440 measures the amplitude R of the demodulated signal obtained from the demodulator 430 and the phase difference θ between the demodulated signal and the current signal or voltage signal (reference signal) of the AC magnetic field generator 300, or The in-phase component X and the quadrature component Y of the demodulated signal obtained from the demodulator 430 with respect to the current signal (reference signal) of the AC magnetic field generator 300 are measured. As a result, the amplitude and phase can be accurately calculated from the in-phase component X and the quadrature component Y, and the phase delay and the like can be evaluated from the quadrature component. Here, the reference signal of the lock-in amplifier is represented by R _ref cos (ωt) (where R _ref takes a positive value), and the demodulated signal having the same angular frequency ω as the reference signal measured by the lock-in amplifier is represented by R cos. When represented by (ωt + θ) (where R is a positive value), the demodulated signal is an alternating current component (∂F _m / ∂z) cos (ω _m t + θ) of the magnetic force gradient acting on the probe 100 as will be described later. The magnetic force gradient amplitude (∂F _m / ∂z) is proportional to the product of the periodically changing probe magnetization amplitude and the DC magnetic field gradient from the magnetic sample 1, so that the probe magnetization When the AC magnetic field is applied to change the sine wave shape at the angular frequency ω, this corresponds to the strength (positive value) of the DC magnetic field gradient. Further, the phase difference θ with the reference signal of the demodulated signal corresponds to the phase difference with the reference signal of the magnetic force gradient, and is used for detecting the polarity of the DC magnetic field from the magnetic sample 1 as will be described later. it can.

On the other hand, the in-phase component X and the quadrature component Y of the amplitude R and phase θ described above and the reference signal R _ref cos (ωt) are related by the following equations (1) and (2).

Therefore, when measuring R cos (θ), which is the amplitude of the in-phase component X with respect to the reference signal of the demodulated signal, it is preferable to adjust the phase of −θ and set θ = 0 to maximize the signal intensity. In particular, when the in-phase component is measured using a lock-in amplifier with the voltage signal of the AC magnetic field generator 300 as a reference signal, the AC magnetic field generator 300 includes an inductance component and a resistance component in terms of an electric circuit. The phase of the current signal for generating the alternating magnetic field is delayed with respect to the voltage signal of the magnetic field generator 300, and therefore phase adjustment is required. On the other hand, when the in-phase component is measured with the lock-in amplifier using the current signal of the AC magnetic field generator 300 as a reference signal, the AC magnetic field is generated in synchronization with the current signal of the AC magnetic field generator 300, so θ = 0. At the timing when the current signal becomes maximum, the gradient of the DC magnetic field from the sample in the direction parallel to the AC magnetic field application direction is detected at the maximum value.

In the magnetic field observation apparatus disclosed in Patent Document 4 and the magnetic profile measurement apparatus described in Patent Document 5, a ferromagnetic material is used for the probe (a soft magnetic material refers to a ferromagnetic material having a low coercive force. ). In a probe made of a ferromagnetic material, when an alternating magnetic field is applied, a magnetic moment caused by spontaneous magnetization generated even when the external magnetic field is zero rotates. Therefore, the magnetic moment also has a component perpendicular to the AC magnetic field direction, except when the magnetic moment is completely parallel to the application direction of the AC magnetic field. Normally, an alternating magnetic field is applied perpendicular to the sample surface, and the magnetic field in the direction perpendicular to the sample surface is measured, and is generated from the sample surface except when the magnetic moment is completely parallel to the alternating magnetic field. In addition to the magnetic force due to the interaction between the vertical component of the magnetic field and the probe magnetization, the magnetic force due to the interaction between the in-plane component of the magnetic field generated from the sample surface and the probe magnetization also acts on the probe, resulting in a detection signal. It will be included. For this reason, in order to measure the vertical magnetic field component and the in-plane magnetic field component separately, complicated phase adjustment processing as in the magnetic profile measuring device described in Patent Document 5 is required for processing the detection signal.

In the magnetic field observation apparatus 1000 according to the present invention, the magnetic probe 100 without magnetic saturation (that is, non-ferromagnetic) is used instead of the ferromagnetic probe with magnetic saturation, so that an AC magnetic field is applied to the probe 100. The probe magnetization occurs only in the direction in which the alternating magnetic field is applied, and does not occur in the direction perpendicular to the direction in which the alternating magnetic field is applied. Thereby, the AC component of the magnetic force that the probe 100 receives from the DC magnetic field from the magnetic sample 1 is derived from only the component in the AC magnetic field application direction of the DC magnetic field from the magnetic sample 1. Therefore, according to the present invention, the measurement direction of the DC magnetic field from the sample can be controlled only by changing the direction of the AC magnetic field applied to the probe, and the signal processing process can be greatly simplified.

(Scanning mechanism 500)
The scanning mechanism 500 is a mechanism that can relatively change the positions of the probe 100 and the magnetic material sample 1. The scanning mechanism 500 causes the probe 100 to scan the scanning area on the surface of the magnetic sample 1. As the scanning mechanism, for example, by moving the sample mounting table on which the magnetic sample 1 is placed by a driving device, the position of the sample mounting table is changed relative to the probe 100, thereby the probe 100. And the magnetic material sample 1 can be a mechanism capable of relatively changing the position. An example of such a mechanism is an XY stage. In addition, it is also possible to employ a scanning mechanism that changes the relative positional relationship between the probe 100 and the magnetic sample 1 by moving the probe 100 with a driving device. As the scanning mechanism 500, a known mechanism (for example, a piezo element) used in a conventional scanning probe microscope or the like can be used.

(Image display device 600)
The image display device 600 is a device that displays a magnetic field distribution image based on DC magnetic field information from the magnetic material sample 1 at each coordinate of the scanning region obtained by scanning the scanning region with the scanning mechanism 500. The image display device 600 is not particularly limited as long as it has a configuration capable of imaging the output signal from the demodulated signal processing device 440 obtained as described above in correspondence with the coordinates. A display device capable of imaging an external input signal as provided in a scanning probe microscope can be used.

(Measurement principle)
The principle of observing a magnetic field with high resolution near the surface of the magnetic material 1 that generates a strong DC magnetic field using the magnetic field observation apparatus 1000 of the present invention will be described below.

As described above, the magnetic force due to the magnetic interaction between the magnetization of the probe 100 and the magnetization of the magnetic sample 1 having a magnetic material as a constituent element has a frequency (non-resonant frequency) different from the resonance frequency of the cantilever. Due to the alternating current component, the vibration frequency of the probe 100 is periodically modulated. The theoretical model is shown in FIG. FIG. 6A schematically shows a state where an alternating magnetic field having a frequency (non-resonant frequency) different from the resonance frequency of the probe 100 is applied to the probe 100 vibrating at a constant frequency. FIG. 6B schematically shows a model in which the movement of the probe 100 is compared to a spring with a weight m attached to the tip.

The frequency modulation phenomenon in which the alternating current component of the magnetic force (non-resonant alternating magnetic force) having a frequency (non-resonant frequency) different from the resonance frequency of the cantilever in the vibration of the probe 100 is a modulation source as shown in FIG. It is derived by considering the motion of the harmonic oscillator (formula (3) below) in which the spring constant periodically changes due to the AC component of the force.

(M: effective mass of the probe 100, t: time, z: amplitude of the probe 100 (the vibration direction of the cantilever is perpendicular to the observation surface and is defined as the z direction), γ: attenuation coefficient, k ₀ : probe 100 Is the intrinsic spring constant of the cantilever 110 before the AC magnetic field is applied to it, Δk: the change amount of the effective spring constant of the cantilever 110 due to the application of the AC magnetic field to the probe 100, ω _m : the excitation angular frequency, F ₀ : amplitude of excitation force, ω ₀ : resonance angular frequency of probe 100)

Here, a case where the cantilever 110 is excited at the resonance frequency ω ₀ is considered.
Δk cos (ω _m t) = k _eff is an effective change in the spring constant due to the alternating force, and Δk corresponds to the amplitude (∂F _m / ∂z) of the magnetic force gradient described above. The solution of equation (3) is as shown in equation (4) below when Δk << k ₀ .

From the above equation (4), it can be seen that frequency modulation occurs in the vibration of the probe 100 using the AC component of the non-resonant alternating magnetic force as the generation source. Here, a paramagnetic material or a superparamagnetic material is used for the probe 100, and an AC magnetic field having an angular frequency ω _m is applied to the probe 100 within a range that does not disturb the magnetization state of the magnetic sample 1. Consider changing the magnetization periodically. Here, a case is considered in which an alternating magnetic field H _z ^ac cos (ω _m t) in a direction (z direction) perpendicular to the sample surface of the magnetic sample 1 is applied to the probe 100. The alternating magnetic field H _z ^ac cos (ω _m t) is generated by the alternating current I ^ac cos (ω _m t) supplied to the alternating magnetic field source. In this case, the measurement direction of the DC magnetic field generated from the magnetic sample 1 is the direction in which the AC magnetic field is applied, that is, the direction perpendicular to the sample surface of the magnetic sample 1 (z direction). The magnetization of the probe 100 receiving the DC magnetic field H _z ^{dc in the} direction perpendicular to the observation surface of the magnetic sample 1 and the DC magnetic field H _x ^dc in the direction parallel to the observation surface is perpendicular to the observation surface of the magnetic sample 1. If the AC magnetic field H _z ^ac cos (ω _m t) in the correct direction (z direction) is changed as shown in the following formula (5), the effective spring constant change k _eff of the cantilever 110 is expressed by the following formula (6). Given.

(M _tip : Magnetization of the probe 100. M _z ^dc : DC magnetization component in the direction perpendicular to the observation surface generated by the DC magnetic field H _z ^{dc in the} direction perpendicular to the observation surface out of the magnetization of the probe 100. M _x ^dc : DC magnetization component in the direction parallel to the observation surface generated by the DC magnetic field H _x ^{dc in the} direction parallel to the observation surface in the magnetization of the probe 100. M _z ^ac : Observation surface in the magnetization of the probe 100 The amplitude of the alternating magnetization in the direction perpendicular to the observation surface generated by the alternating magnetic field H _z ^{ac in the} direction perpendicular to.

Here, the equation is developed using the fact that the probe magnetization can detect a magnetic field in the same direction as the magnetization direction in principle.

The spatial change of the alternating magnetic field applied to the probe 100 is reduced, and the product of the spatial change of the alternating magnetic field applied to the probe 100 and the intensity of the direct current component of the magnetization of the probe 100 is reduced to the following equation (7) Is satisfied, the second term that changes at the angular frequency ω _m in equation (6) is expressed by equation (8) below.

Therefore, after demodulating the frequency modulation signal of the vibration of the probe 100 generated by applying the alternating magnetic field under these conditions by the demodulator 430, the demodulated signal is demodulated using the demodulated signal processing device (lock-in amplifier) 440. By using the output of the alternating current power supply 310 provided in the alternating current magnetic field generator 300 as a reference signal and detecting the lock-in at the angular frequency ω _m of the alternating current power supply 310, the vertical magnetic field H _z ^dc from the magnetic material sample 1 is detected. It can be seen that the magnetic field gradient (∂ ² H _z ^dc / ∂ _z ² ) can be measured near the sample surface.

Here, the sign (upward and downward polarity) of H _z ^dc reflects the polarity of the surface magnetic pole (N pole, S pole) of the magnetic sample 1, and when the sign is reversed, the effective spring constant changes. The component that changes at the angular frequency ω _m of k _eff changes as in the following equation (9), and the phase changes by 180 °.

Therefore, by identifying two measurement locations that are 180 ° out of phase, the direction of H _z ^dc (upward and downward) generated from the magnetic sample 1 is detected, and the polarity of the surface magnetic pole (N pole, S pole) ) Can be identified directly.

In the above equation (7), since the left side is a necessary signal and the right side is not necessary, it corresponds to noise. Therefore, for example, in order to set the signal to noise ratio to 9: 1, it is necessary to satisfy the following expression (10).

In the above formula (10), (∂ ² H _z ^dc / ∂ _z ² ) reflects the magnetic non-uniformity of the magnetic material sample 1, whereas it changes on the nanometer scale with respect to the measurement location. Thus, (∂ ² H _z ^ac / ∂z ² ) reflects the size of the AC electromagnet and changes on a millimeter scale with respect to the measurement location, so noise in the observation of the magnetic domain structure (the right side of equation (7) above) ) Is usually small.
In the range where the distance between the probe samples is small, the contribution of the magnetic pole at the tip of the probe 100 is large, so that the probe behaves as a single magnetic pole probe. In this case, the above equation (8) becomes the following equation (11).

(Q _tip ^ac : amplitude of an AC magnetic pole generated by an AC magnetic field among the magnetic poles at the tip of the probe 100.)

<3. Magnetic field observation method>
The magnetic field observation method of the present invention is a magnetic field observation method for observing a DC magnetic field leaking from a magnetic material sample, and includes (i) an excitation process; (ii) an AC magnetic field application process; (iii) a demodulation process; iv) a demodulated signal processing step; and (v) a scanning step. Preferably, (vi) a magnetic field distribution image display step is further included.
The magnetic field observation method of the present invention can be performed using, for example, the magnetic field observation apparatus 1000 of the present invention described above. Hereinafter, each step will be described with reference to FIG.

(I) The excitation step is a step of exciting a cantilever having a magnetic probe without magnetic saturation at one end. The excitation process can be performed by the exciter 200 described above.

(Ii) The AC magnetic field applying step is a step of applying frequency modulation to the excitation vibration of the cantilever by applying an AC magnetic field having a magnitude that does not reverse the magnetization of the magnetic sample to the probe and periodically changing the magnetization of the probe. It is. The AC magnetic field application process can be performed by the AC magnetic field generator 300 described above.

(Iii) The demodulation step is a step of detecting the vibration of the probe and demodulating a signal corresponding to the AC component of the magnetic force generated between the probe and the observation sample from the detected signal. The demodulation process can be performed by the vibration sensor 400 and the demodulator 430 described above.

(Iv) The demodulated signal processing step is a step of obtaining DC magnetic field information from the signal demodulated in the demodulating step and the voltage signal of the AC magnetic field generator. The demodulated signal processing step can be performed by the demodulated signal processing device 440 described above.

(V) The scanning step is a step of causing the probe to scan the scanning region on the surface of the magnetic sample. The scanning process can be performed by the scanning mechanism 500 described above.

(Vi) The magnetic field distribution image display step is a step of displaying, on the image display device, a magnetic field distribution image based on DC magnetic field information at each coordinate of the scanning region obtained by scanning the scanning region with the scanning mechanism. The magnetic field distribution image display step can be performed by the image display device 600 described above.

The magnetic field observation method of the present invention can be preferably used for magnetic field observation of a sample (for example, a permanent magnet) that generates a strong DC magnetic field. Further, (ii) the alternating magnetic field generated by the alternating magnetic field generator 30 in the alternating magnetic field application step preferably has a small spatial change. Specifically, the DC component of the magnetization at the tip of the probe 100 (that is, the magnetization due to the DC magnetic field leaking from the magnetic sample 1) and the spatial change gradient of the AC magnetic field applied from the AC magnetic field generator 300 to the probe 100. Is the space between the AC component of the magnetization at the tip of the probe 100 (that is, the magnetization fluctuation due to the AC magnetic field applied from the AC magnetic field generator 300) and the DC magnetic field applied from the magnetic sample 1 to the probe 100. It is preferably smaller than the product of the change gradient.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples.

<Example 1>
This is an example in which the probe for a magnetic force microscope of the present invention in a form having an Fe—Mn solid solution type paramagnetic material as a magnetic film was produced.
In the sputtering apparatus of FIG. 4, Fe and Mn are simultaneously sputtered using a Fe target as the ferromagnetic element target 44 and a Mn target as the non-magnetic element target 45, so that the Si can be fixed to one end of the cantilever. A Fe—Mn solid solution paramagnetic thin film (Fe ₆₇ Mn ₃₃ , film thickness 100 nm) was formed on the surface of the core member. FIG. 7 shows the results of magnetic property evaluation of a paramagnetic thin film formed on a Si substrate with a thermal oxide film under the same conditions. The composition analysis of the thin film was performed by energy dispersive X-ray spectroscopy (EDX). Magnetic property evaluation was performed using a vibrating sample magnetometer VSM-5S type (manufactured by Toei Kogyo Co., Ltd.) under conditions of a temperature of 25 ° C. and an external magnetic field of −20 kOe to +20 kOe.

As shown in FIG. 7, the formed Fe—Mn solid solution paramagnetic thin film did not saturate until the strength of the external magnetic field reached 20 kOe. Moreover, it did not have remanent magnetization or magnetic hysteresis. Its initial magnetic susceptibility was 1.2 × 10 ⁻⁷ H / m.

<Example 2>
This is an example in which the magnetic force microscope probe of the present invention in a form having a Fe—Mo—B-based amorphous paramagnetic material as a magnetic coating was produced.
In the sputtering apparatus of FIG. 4, by using the Fe target as the ferromagnetic element target 44 and the Mo target with the B sheet attached as the nonmagnetic element target 45, Fe, Mo, and B are simultaneously sputtered, An attempt was made to form a Fe—Mo—B amorphous paramagnetic thin film (thickness: 100 nm) on the surface of a Si core member fixed to one end. FIGS. 8A to 8I show the results of evaluating the composition and magnetic properties of the magnetic thin film formed on the Si substrate with the thermal oxide film under the same conditions under the same conditions as in Example 1. FIG.

In FIG. 8, the thin films of (a) and (b) in which the contents of Mo and B, which are non-magnetic elements, are too small, are comparative examples in which magnetization is saturated before the intensity of the external magnetic field reaches 20 kOe. It is. On the other hand, the thin films (c) to (i) in which the contents of Mo and B that are nonmagnetic elements were sufficient did not saturate until the external magnetic field strength reached 20 kOe. There was no residual magnetization or magnetic hysteresis. In particular, (d) Fe ₈₆ Mo _7.5 B _6.5 amorphous paramagnetic thin film has an initial magnetic susceptibility (1.4 × 10 ⁻⁷ H / m) and linearity of magnetization response to an external magnetic field. Both were the best. Such a probe having excellent linearity of magnetization response is particularly suitable for magnetic domain observation with an alternating magnetic force microscope of a magnetic sample that generates a strong DC magnetic field (10 kOe or more).

<Example 3>
This is an example in which the probe for a magnetic force microscope of the present invention in a form having an Ag—Co-based granular superparamagnetic material as a magnetic film is produced.
In the sputtering apparatus of FIG. 4, by using a Co target as the ferromagnetic element target 44 and an Ag target as the nonmagnetic element target 45, Co and Ag are simultaneously sputtered, so that Si is fixed to one end of the cantilever. An attempt was made to form an Ag—Co granular superparamagnetic thin film (film thickness: 100 nm) on the surface of the core member. The distance (80 mm, 100 mm, or 120 mm) between the Ag target 45 and the rotation holding table 42 and the power applied to each target (100 to 200 W for the

Ag target

45, 50 to 150 W for the Co target 44) The composition ratio of Co and Ag (Co content: 6 to 21% by volume based on the total amount of magnetic material, balance Ag) and the film formation rate (0.1 to 0.85 nm / sec) were adjusted by changing . FIG. 9 shows the results of evaluating the composition and magnetic properties of the magnetic thin film formed on the Si substrate with the thermal oxide film under the same conditions under the same conditions as in Example 1. In FIG. 9, the value of the initial magnetic susceptibility indicated by the sample is added below each data point corresponding to the thin film sample that is determined not to saturate until reaching an external magnetic field of 20 kOe and exhibits superparamagnetism. ing. A data point in the region of “with hysteresis” indicates that the magnetization characteristic of the sample showed hysteresis, that is, the sample contained a ferromagnetic phase.

As can be seen from FIG. 9, as a general tendency, the higher the Co content of the ferromagnetic material, the higher the initial magnetic susceptibility of the sample. In particular, the higher the Co content, the more the initial magnetic susceptibility changes in the composition. It reacted sensitively. Even if the content of Co, which is a ferromagnetic element, is high, a superparamagnetic material without hysteresis can be formed by increasing the film formation rate. As a result, the maximum value of the obtained initial magnetic susceptibility was 4.0 × 10 ⁻⁶ H / m. Such a probe having an extremely high initial magnetic susceptibility is particularly suitable for measuring an absolute value including positive and negative of a DC magnetic field generated from a magnetic sample.

FIG. 10 is a magnetization curve (FIG. 10A) of an Ag ₇₉ Co ₂₁ thin film (1) (initial magnetic susceptibility 4.0 × 10 ⁻⁶ H / m) formed at a film formation rate of 0.80 nm / sec. FIG. 10B is an enlarged view of the vicinity of the origin.) And an Ag ₈₅ Co ₁₅ thin film (2) (initial magnetic susceptibility of 3.0 × 10 ⁻⁶ H) formed at a film formation rate of 0.20 nm / sec. / M) magnetization curve (FIG. 10 (c), FIG. 10 (d) is an enlarged view of the vicinity of the origin). As can be seen from FIG. 10, the Ag ₈₅ Co ₁₅ thin film formed at a low film formation rate of 0.20 nm / sec showed hysteresis and remanent magnetization, that is, had a ferromagnetic phase (FIG. 10C). And (d))), the Ag ₇₉ Co ₂₁ thin film formed at a high film formation rate of 0.80 nm / sec has a higher content of Co, which is a ferromagnetic element, The property of the ferromagnetic phase was hardly shown (see FIGS. 10A and 10B). In addition, the average value of the sphere conversion diameter by the image analysis method of Co particles in the Ag ₇₉ Co ₂₁ thin film (1) formed at a film formation rate of 0.80 nm / sec was 15 nm. This value is obtained by observing the surface of the thin film with a scanning electron microscope (SEM) at a magnification of 100,000 to 200,000 by secondary electron detection, and showing an area equal to the area occupied by Co particles in the SEM image. This is a value obtained by calculating the diameter (sphere equivalent diameter) of the circle to have and calculating the arithmetic average of 100 or more Co particles in the same thin film sample.

FIG. 11 shows the temperature dependence of the initial magnetic susceptibility of an Ag—Co superparamagnetic thin film re-fabricated under the same conditions as the Ag ₇₉ Co ₂₁ thin film (1) shown in FIGS. 9 and 10 (deposition rate 0.80 nm / sec). And the temperature dependence of the initial magnetic susceptibility of an Ag-Co superparamagnetic thin film remanufactured under the same conditions as the Ag ₈₃ Co ₁₇ thin film (3) (deposition rate 0.54 nm / sec) shown in FIG. It is a figure to do. FIGS. 11A and 11C are graphs showing the temperature dependence of the initial magnetic susceptibility, and FIGS. 11B and 11D are graphs showing the temperature dependence of magnetization in the external magnetic field 20 kOe.

As shown in FIG. 11 (a), the Ag-Co superparamagnetic thin film re-fabricated under the same conditions as the Ag ₇₉ Co ₂₁ thin film (1) (deposition rate 0.80 nm / sec) has a temperature range of 25 to 200 ° C. (Measurement points were 5 points of 25 ° C., 50 ° C., 100 ° C., 150 ° C., and 200 ° C.). That is, in the temperature range of 25 to 200 ° C., the initial magnetic susceptibility showed a slight negative correlation with temperature, showing a maximum value at 25 ° C. and a minimum value at 200 ° C. This means that the thin film contains a slight amount of ferromagnetic phase. However, the change width (difference between the maximum value and the minimum value) was within ± 10% with respect to the arithmetic average value of the five measured values. The same was true for the magnetization in the external magnetic field 20 kOe (FIG. 11B).

Further, as shown in FIG. 11 (c), the Ag—Co superparamagnetic thin film re-fabricated under the same conditions as the Ag ₈₃ Co ₁₇ thin film (3) (deposition rate 0.54 nm / sec) is in the temperature range of 25 to 200 ° C. (Measurement points were 5 ° C. at 25 ° C., 50 ° C., 100 ° C., 150 ° C., and 200 ° C.) and did not have temperature dependency. That is, no consistent tendency is observed in the measured values of the initial susceptibility and the magnetization in the external magnetic field of 20 kOe in the temperature range of 25 to 200 ° C., and the fluctuation range thereof is also the arithmetic average value of the above five measured values. Within ± 10%. The same was true for the magnetization in the external magnetic field of 20 kOe (FIG. 11D).

The magnetic susceptibility and magnetization have temperature dependence is a typical property of a ferromagnetic material, which is unavoidable with conventional ferromagnetic probes. However, according to the superparamagnetic probe of the present invention, it is possible to provide a probe having little or no temperature dependence. Such a probe having substantially no temperature dependence of magnetic properties is particularly suitable for evaluating the domain structure of a permanent magnet at a high temperature.

In FIG. 11, the measured value of the initial magnetic susceptibility at 25 ° C. is different from the corresponding measured value described in FIG. 9 because of the following reason. Due to the limitations of the sputtering apparatus, when simultaneously sputtering Ag and Co, the Co target had to be arranged at a position shifted laterally from the front of the substrate holder. Therefore, depending on the position of the substrate in the holder circumferential direction on the rotating substrate holder at the start of sputtering, the average distance between the substrate and the Co target varies slightly from the start to the end of sputtering. It was inevitable to do. Therefore, even if the other film forming conditions are the same, the composition of the produced Ag—Co superparamagnetic thin film may not completely match the compositions of the thin films (1) and (3). As described above with reference to FIG. 9, the thin films (1) and (3) are in a region where the initial magnetic susceptibility is sensitive to the composition. Accordingly, the deviation of the value of the initial magnetic susceptibility at 25 ° C. shown in FIGS. 11A and 11C from the value in FIG. 9 is that of the substrate in the circumferential direction of the holder on the rotating substrate holder at the start of sputtering. This is considered to reflect a slight shift in the composition of the thin film due to the fact that the arrangement position could not be completely reproduced.
In FIGS. 11A and 11C, the initial magnetic susceptibility is markedly increased in the temperature range exceeding 200 ° C. This is a result of the change in the fine structure of the granular superparamagnetic thin film at a high temperature. It is believed that there is.

<Example 4>
Using the magnetic field observation apparatus of the present invention (see FIG. 5), a DC magnetic field leaking from a permanent magnet thin film sample (FePt—MgO-based permanent magnet film, film thickness 300 nm, vertical coercive force: 8 kOe) was observed. The magnetic field observation apparatus of the present invention is based on a commercially available MFM (scanning probe microscope, AFM-5400L manufactured by Hitachi High-Tech Science Co., Ltd.), and an AC electromagnet manufactured using a silicon steel sheet as an AC magnetic field generator and the AC An AC voltage power source for supplying power to the electromagnet was added, and an FM demodulator (manufactured by Nanosurf, easyPLL) was added as a demodulator. The AC electromagnet was installed under the MFM sample mounting table so that an AC magnetic field was applied perpendicular to the observation surface of the sample. The amplitude of the AC magnetic field applied from the AC electromagnet to the probe was 2.2 kOe, and the frequency was 89 Hz. The probe 100 for magnetic force microscope according to the present invention described above was used as the probe. A granular superparamagnetic material using Si as the nonmagnetic element constituting the core member 10, Co as the ferromagnetic element, and Ag as the nonmagnetic element was used for the magnetic coating 30. The film thickness of the magnetic coating 30 was about 100 nm. The initial magnetic susceptibility of the magnetic coating 30 was 2.2 × 10 ⁻⁶ H / m. The probe 100 did not exhibit magnetization saturation until reaching an external magnetic field of 20 kOe, and had no residual magnetization or magnetic hysteresis. The magnetic coating 30 is formed by simultaneously sputtering Co and Ag on the surface of a Si probe fixed to one end of a cantilever using a Co target and an Ag target simultaneously in a commercially available sputtering apparatus. It was done by doing. The Co content in the thin film was about 18% by volume, and the film formation rate was about 0.56 nm / sec. The distance between the probe and the observation surface of the magnetic sample at the time of observation was 10 nm.

The magnetization of the superparamagnetic probe was periodically changed by the AC magnetic field from the AC electromagnet without changing the magnetic moment of the permanent magnet thin film. After acquiring the surface shape image of the observation surface of the permanent magnet thin film by scanning using the Tapping-Lift mode, scanning using the Lift mode while applying an alternating magnetic field, the frequency-modulated detection signal of the probe vibration Is demodulated using an FM demodulator, the demodulated signal is input to a lock-in amplifier, and the voltage signal of the AC voltage power source connected to the AC electromagnet is used as a reference signal to determine the amplitude of the demodulated signal and the phase difference with respect to the reference signal. By measuring, DC magnetic field information of the permanent magnet thin film was obtained.

FIG. 12 shows the observation results near the surface of the permanent magnet thin film. FIG. 12A is a surface shape image of the scanned region. FIG. 12B is an image of the amplitude of the magnetic force gradient signal corresponding to the gradient strength of the DC magnetic field (vertical magnetic field) perpendicular to the observation surface of the permanent magnet thin film, and FIG. The phase of the magnetic force gradient signal corresponding to the magnetic field gradient is imaged. FIG. 12B shows an image in which the bright part is surrounded by a linear dark part, and FIG. 12C shows a binary image of the bright part and the dark part. 12D shows the line profile of the image of FIG. 12B, and FIG. 12E shows the line profile of the image of FIG. 12C.

Looking at the line profiles (FIGS. 12D and 12E), in FIG. 12D, in the boundary portion where the phase is inverted by 180 ° in the phase line profile of FIG. It can be seen that the amplitude signal corresponding to the direction of the direct current magnetic field gradient is zero. In FIG. 12 (e), the bright part corresponds to the part where the direction of the vertical magnetic field is upward, and the dark part corresponds to the part where the direction of the vertical magnetic field is downward, with this boundary part as a boundary. ) Exists on the surface, and in the dark part, a negative magnetic pole (S pole) exists on the surface. Therefore, simply applying an AC magnetic field parallel to the DC magnetic field measurement direction to the superparamagnetic probe makes it possible to perform DC magnetic field measurement with the AC magnetic field direction as the measurement direction. It can be seen that this is possible without performing phase adjustment processing. In FIGS. 12C and 12E, the gradient of the DC magnetic field (in-plane magnetic field) in the direction parallel to the sample surface is maximum at the boundary where the phase is inverted by 180 °.

In the magnetic field observation apparatus disclosed in Patent Document 4 and the magnetic profile measurement apparatus described in Patent Document 5, a ferromagnetic material is used for the probe (a soft magnetic material refers to a ferromagnetic material having a low coercive force. ). In a ferromagnetic material, when an alternating magnetic field is applied, a magnetic moment caused by spontaneous magnetization generated even when the external magnetic field is zero rotates. Thus, except when the magnetic moment is completely parallel to the alternating magnetic field, the magnetic moment also has a component perpendicular to the alternating magnetic field direction. Normally, an alternating magnetic field is applied perpendicular to the sample surface, and the magnetic field in the direction perpendicular to the sample surface is measured, and is generated from the sample surface except when the magnetic moment is completely parallel to the alternating magnetic field. In addition to the magnetic force due to the interaction between the vertical component of the magnetic field and the probe magnetization, the magnetic force due to the interaction between the in-plane component of the magnetic field generated from the sample surface and the probe magnetization also acts on the probe, resulting in a detection signal. It will be included. For this reason, in order to measure the vertical magnetic field component and the in-plane magnetic field component separately, complicated phase adjustment processing as in the magnetic profile measuring device described in Patent Document 5 is required for processing the detection signal.

When the magnetic force microscope probe 100 of the present invention without magnetic saturation (that is, not ferromagnetic) is used as an alternating magnetic force microscope, instead of a ferromagnetic probe with magnetic saturation as the probe, an alternating magnetic field is applied to the probe 100. The probe magnetization due to the application of is generated only in the direction in which the alternating magnetic field is applied, and does not occur in the direction perpendicular to the direction in which the alternating magnetic field is applied. Thereby, the AC component of the magnetic force that the probe 100 receives from the DC magnetic field from the magnetic sample 1 is derived from only the component in the AC magnetic field application direction of the DC magnetic field from the magnetic sample 1. Therefore, by using the magnetic force microscope probe of the present invention for an alternating magnetic force microscope, signal processing in the magnetic force microscope can be greatly simplified.

As described above, according to the probe for a magnetic force microscope of the present invention, the probe can be adsorbed to the sample even in the magnetic field observation near the surface of the magnetic sample that generates a strong DC magnetic field such as a permanent magnet. In addition, it was shown that the magnetic field can be observed with high spatial resolution, and further, the polarity of the magnetic pole on the surface of the magnetic material sample can be detected. Further, according to the magnetic field observation apparatus and magnetic field observation method of the present invention, it is possible to observe a magnetic field with high spatial resolution in the vicinity of the surface of a magnetic sample that generates a strong DC magnetic field such as a permanent magnet, It was shown that the polarity of the magnetic pole on the surface of the magnetic material sample can be detected. The magnetic force microscope probe of the present invention is suitable for, for example, observation of magnetic domains of a strong magnetic field generation sample such as a permanent magnet sample by an alternating magnetic force microscope, measurement of an absolute value including positive / negative of a DC magnetic field generated from a magnetic sample, and the like. Can be used. The magnetic field observation apparatus and magnetic field observation method of the present invention can be suitably used for magnetic domain observation of a permanent magnet sample, for example.

DESCRIPTION OF SYMBOLS 1 Magnetic body sample 10 Core member 20 Cantilever 30 Magnetic film 41 Chamber 42 Rotation holding stand 43 Rotation drive shaft 44 Ferromagnetic element target 45 Nonmagnetic element target 100 Probe 110 Cantilever 200 Exciter 300 AC magnetic field generator 310 AC current power supply 320 Coil 400 Vibration sensor 410 Light source 420 Optical displacement sensor 430 Demodulator (FM demodulator)
440 Demodulated signal processing device (lock-in amplifier)
500 Scanning mechanism 600 Image display device 1000 Magnetic field observation device

Claims

Comprising at least one magnetic material,
Magnetization is not saturated when a magnetic field is applied over a temperature range of at least 10-30 ° C.,
(A) the magnetic material is a solid solution of one or more ferromagnetic elements and one or more nonmagnetic elements;
(B) the magnetic material is an amorphous magnetic material containing one or more ferromagnetic elements and one or more nonmagnetic elements; or (c) the magnetic material is one or more ferromagnetic materials. A magnetic material comprising a body particle and at least one non-magnetic material, wherein the ferromagnetic particle is supported by being dispersed in the non-magnetic material. Probe.
2. The probe for a magnetic force microscope according to claim 1, wherein the probe does not have residual magnetization over a temperature range of at least 10 to 30 ° C. under a condition where no magnetic field is applied.
3. The magnetic force microscope probe according to claim 1, wherein the magnetic material has an initial magnetic susceptibility of 3 × 10 −8 H / m or more over a temperature range of at least 10 to 30 ° C.
Satisfy the requirements of (a) or (b),
The ferromagnetic element is one or more ferromagnetic elements selected from the group consisting of Ni, Fe, and Co;
The nonmagnetic element is at least one selected from the group consisting of Ti, V, Cr, Mn, Cu, Zn, Zr, Nb, Mo, Ta, W, B, Al, C, O, N, and Si. A non-magnetic element,
The probe for a magnetic force microscope according to any one of claims 1 to 3.
Satisfy the requirements of (a) or (b),
The probe for a magnetic force microscope according to claim 1, wherein the magnetic material exhibits paramagnetism or superparamagnetism.
Satisfy the requirements of (c) above,
For the total amount of the magnetic material,
The content of the ferromagnetic particles is 10 to 45% by volume,
The content of the nonmagnetic material is 55 to 90% by volume.
The probe for a magnetic force microscope according to any one of claims 1 to 3.
Satisfy the requirements of (c) above,
The probe for a magnetic force microscope according to any one of claims 1 to 3 and 6, wherein an average value of spherical equivalent diameters of the ferromagnetic particles by an image analysis method is 30 nm or less.
Satisfy the requirements of (c) above,
The ferromagnetic particles are particles of one or more ferromagnetic elements selected from the group consisting of Ni, Fe, and Co;
The nonmagnetic material is Au, Ag, Cu, silicon dioxide, titanium oxide, tungsten oxide, chromium oxide, cobalt oxide, tantalum oxide, boron oxide, magnesium oxide, cerium oxide, yttrium oxide, nickel oxide, aluminum oxide, ruthenium oxide. , One or more nonmagnetic materials selected from the group consisting of rare earth element oxides and carbon,
The probe for a magnetic force microscope according to any one of claims 1 to 3, 6, and 7.
Satisfy the requirements of (c) above,
The probe for a magnetic force microscope according to any one of claims 1 to 3 and 6 to 8, wherein the magnetic material exhibits superparamagnetism.
Satisfy the requirements of (c) above,
The probe for a magnetic force microscope according to any one of claims 1 to 3 and 6 to 9, wherein the magnetic susceptibility has substantially no temperature dependence in a temperature range of 25 to 200 ° C.
Satisfy the requirements of (c) above,
The magnetic force microscope probe according to any one of claims 1 to 3 and 6 to 10, wherein an initial magnetic susceptibility of the magnetic material is 2 × 10 -7 H / m or more over a temperature range of at least 10 to 30 ° C. needle.
A core member made of one or more non-magnetic materials;
The probe for a magnetic force microscope according to any one of claims 1 to 11, further comprising a coating of the magnetic material that covers at least a part of a surface of the core member.
A magnetic field observation apparatus for observing a DC magnetic field leaking from a magnetic sample,
A cantilever having a magnetic probe at one end that has no magnetic saturation and generates a magnetic moment in the direction of the applied magnetic field;
An exciter for exciting the cantilever;
An alternating magnetic field generator for applying frequency modulation to the excitation vibration of the cantilever by applying an alternating magnetic field of a magnitude that does not reverse the magnetization of the magnetic sample to the probe and periodically varying the magnetization of the probe; ,
A vibration sensor for detecting the vibration of the probe;
A demodulator that demodulates a signal corresponding to an alternating current component of the magnetic force generated between the probe and the magnetic sample from the detection signal of the vibration sensor;
A demodulated signal processing device for obtaining information on the DC magnetic field from the demodulated signal obtained from the demodulator and the voltage signal of the AC magnetic field generator;
A scanning mechanism for causing the probe to scan a scanning region on the surface of the magnetic sample,
13. A magnetic field observation apparatus for a magnetic field generation sample, wherein the magnetic probe is the probe for a magnetic force microscope according to claim 1.
The demodulator
(A) The frequency of the detection signal of the vibration sensor is demodulated, or
(B) Measure the intensity of the sideband spectrum included in the detection signal of the vibration sensor,
The magnetic field observation apparatus according to claim 13.
The demodulated signal processing device comprises:
(X) measuring the amplitude of the demodulated signal obtained from the demodulator and the phase difference between the demodulated signal and the current signal or voltage signal of the AC magnetic field generator, or
(Y) measuring the in-phase component and the quadrature component of the demodulated signal obtained from the demodulator with respect to the current signal of the AC magnetic field generator;
The magnetic field observation apparatus according to claim 13 or 14.
The magnetic field observation apparatus according to any one of claims 13 to 15, wherein the AC magnetic field generation mechanism applies the AC magnetic field in the same direction as a direction of a component to be measured of the DC magnetic field.
The magnetic field observation apparatus according to any one of claims 13 to 16, wherein the magnetic sample is a permanent magnet.
The image display device according to any one of claims 13 to 17, further comprising an image display device that displays a magnetic field distribution image based on information on the DC magnetic field at each coordinate of the scanning region obtained by scanning the scanning region with the scanning mechanism. The magnetic field observation apparatus according to claim 1.
A magnetic field observation method for observing a DC magnetic field leaking from a magnetic sample,
Exciting a cantilever having a magnetic probe at one end that has no magnetic saturation and generates a magnetic moment in the direction of the applied magnetic field;
Applying an alternating magnetic field of a magnitude that does not reverse the magnetization of the magnetic sample to the probe, and periodically modulating the magnetization of the probe, thereby frequency-modulating the excitation vibration of the cantilever;
Detecting the vibration of the probe and demodulating a signal corresponding to an alternating current component of the magnetic force generated between the probe and the magnetic sample from the detection signal of the vibration of the probe;
Obtaining the DC magnetic field information from the demodulated signal and the AC magnetic field generator voltage signal;
Scanning the scanning region on the surface of the magnetic material sample with the probe,
A magnetic field observation method for a magnetic field generation sample, wherein the magnetic probe is the probe for a magnetic force microscope according to any one of claims 1 to 12.
The magnetic field observation method according to claim 19, wherein the alternating magnetic field is applied in the same direction as a direction of a component to be measured of the direct magnetic field.
The magnetic field observation method according to claim 19 or 20, wherein the magnetic sample is a permanent magnet.
The method further comprises a step of displaying, on an image display device, a magnetic field distribution image obtained by scanning the scanning region with the scanning mechanism and based on information on the DC magnetic field at each coordinate of the scanning region. The magnetic field observation method according to any one of the above.