JP2012198192A - Magnetic force microscope and high spatial resolution magnetic field measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problems of conventional magnetic force microscopes: that as the primary resonance frequency of a cantilever is varied during probe scanning, the phase of a modulation frequency signal is varied and it is difficult to obtain a magnetic field distribution with phase information; that a measuring time becomes long due to a low excitation frequency of about 100 Hz; and that as a FM modulation signal which is an indirect signal is measured, a S/N ratio is hard to be increased.SOLUTION: An inventive magnetic force microscope includes: a cantilever 2 with a probe 1 having a magnetic material; a first oscillator 4 exciting with a first resonance frequency; a displacement detection circuit 7; a fine motion element 16; a z-axis drive part 12 for driving the fine motion element 16; a second oscillator 13 exciting with a second resonance frequency; and a lock-in amplifier 21 inputting a displacement signal and a reference signal. The z-axis drive part 12 allows the probe 1 to approach a magnetic recording head 8 based on the displacement signal and the first resonance frequency, and the lock-in amplifier 21 generates magnetic field data based on the displacement signal and the reference signal.

Description

  The present invention relates to a magnetic force microscope that measures a magnetic field distribution and uneven shape on a sample surface, and a high spatial resolution magnetic field measurement method that measures the magnetic field distribution with high spatial resolution.

  In order to increase the density of magnetic recording devices such as hard disks, a technique for imaging the magnetic distribution of magnetic characteristics of the magnetic recording head and the magnetic thin film with high spatial resolution is in progress. In order to achieve this, several techniques have been proposed.

  In Non-Patent Documents 1 to 5, in order to directly observe an alternating magnetic field, a configuration of a magnetic force microscope using a frequency modulation technique and an alternating current was applied to a magnetic recording head of a hard disk using the magnetic force microscope. In this case, the result of measuring an alternating magnetic field image generated from the magnetic recording head is described.

  Patent Document 1 describes a technique for applying an external magnetic field having a frequency different from the resonance frequency of a cantilever of a magnetic force microscope to a magnetic recording head that is a sample to be measured in order to shorten the measurement time by the magnetic force microscope. Has been.

JP 2010-175534 A

H. Saito, H. Ikeya, G. Egawa, S. Ishio and S. Yoshimura, `` Magnetic force microscopy of alternating magnetic field gradient by frequency modulation of tip oscillation '', JOURNAL OF APPLIED PHYSICS, 105, 07D524 (2009) W. Lu, Z. Li, K. Hatakeyama, G. Egawa, S. Yoshimura and H. Saito, `` High resolution magnetic imaging of perpendicular magnetic recording head using frequency-modulated magnetic force microscopy with a hard magnetic tip '', APPLIED PHYSICS LETTERS 96, 143104 (2010) Tanaka, Yanagiuchi, Majima, 71st JSAP Scientific Lecture, 17-P12-12, 62 (2010) H. Saito, W. Lu, K. Hatakeyama, G. Egawa and S. Yoshimura `` High frequency magnetic field imaging by frequency modulated magnetic force microscopy '', JOURNAL OF APPLIED PHYSICS 107, 09D309 (2010) W. Lu, K. Hatakeyama, G. Egawa, S. Yoshimura and H. Saito, `` Characterization of Magnetic Field Distribution in a Trailing-Edge Shielded Head by Frequency-Modulated Magnetic Force Microscopy '', IEEE TRANSACTIONS ON MAGNETICS, VOL. 46 , NO. 6, JUNE 2010

  In the magnetic force microscope disclosed in Non-Patent Documents 1 to 5, first, the uneven shape of the surface of the sample to be measured is measured. In this conventional magnetic force microscope, in order to measure the uneven shape of the surface of the sample to be measured, the cantilever is vibrated at the primary resonance frequency and attached to the tip of the cantilever so that the vibration amplitude at the tip of the cantilever is constant. The surface of the sample to be measured is scanned while controlling the distance between the probe and the sample to be measured. Next, using the data of the surface roughness of the sample to be measured memorized in the first scan, the magnetic field magnitude and phase change state with the distance between the probe and the sample to be measured kept constant Is measured along the first scan line. Here, since the sample to be measured is excited at a constant excitation frequency, the detected signal is obtained by frequency modulation (hereinafter also referred to as FM) of the excitation frequency with the primary resonance frequency of the cantilever. . This signal is FM demodulated, the excitation frequency is input to the lock-in amplifier as a reference frequency, and lock-in detection is performed to obtain magnetic field distribution data on the surface of the sample to be measured.

  However, in the conventional magnetic force microscope described above, the FM signal also fluctuates due to the fluctuation of the primary resonance frequency of the cantilever during scanning of the probe, and as a result, the phase of the FM signal that is the detection signal fluctuates. For this reason, the conventional magnetic force microscope has a drawback that it is difficult to obtain an R cos θ image indicating the magnitude and phase of the magnetic field. In the conventional magnetic force microscope, it is possible to improve the phase fluctuation by incorporating a phase-locked loop in the measurement system, but the apparatus becomes complicated and expensive. In addition, since the excitation frequency for the sample to be measured is as low as about 100 Hz to 1 kHz, there is a disadvantage that the measurement throughput per unit time is poor and the measurement time becomes long. Note that this problem can be improved by simply increasing the excitation frequency for the sample to be measured, but in order to increase the excitation frequency for the sample to be measured, the primary resonance frequency, which is the modulation frequency, must be increased. In this case, the frequency response of the optical lever for detecting the displacement of the cantilever must be greatly improved, which causes a measurement system problem as pointed out in Non-Patent Document 4. Further, there is a problem that it is theoretically difficult to increase the S / N ratio by measuring an indirect signal such as an FM signal.

  Further, in the magnetic force microscope disclosed in Patent Document 1, the cantilever is vibrated at the primary resonance frequency, and is different from the resonance frequency of the cantilever and is covered at a frequency that is an integral multiple (or an integral multiple / 2) of the resonance frequency of the cantilever. The measurement sample is excited. Thereby, the step response at the time of movement of the measurement position is improved, and the measurement time is shortened. However, in this conventional magnetic force microscope, since the excitation frequency of the sample to be measured is excited at a frequency that is not the resonance frequency of the cantilever, the Q of the measurement system is low and the gain does not increase, resulting in the S / N of the detection signal. There is a disadvantage that the ratio cannot be increased.

  Accordingly, an object of the present invention is to provide a magnetic force microscope that can obtain magnetic field distribution data having a high S / N ratio in a short measurement time while eliminating the need for a phase-locked loop.

  In order to solve the above-described problems, a magnetic force microscope according to the present invention includes a cantilever having a tip made of a magnetic material or a probe coated with a magnetic material or formed into a thin film at the tip, and the cantilever at a first resonance frequency of the cantilever. The first oscillator to be excited, the displacement detector for detecting the displacement of the tip of the cantilever, and the fine movement for fixing the sample on the upper surface and moving the probe closer to, away from, or moving the measurement position An element, a drive unit for driving the fine movement element, a second oscillator for exciting the sample at the second resonance frequency of the cantilever, a displacement signal output from the displacement detector and a reference signal which is the second resonance frequency And a small signal amplifier. Then, the driving unit drives the fine movement element based on the displacement of the tip of the cantilever detected by the displacement detector and the first resonance frequency, thereby moving the probe closer to or away from the sample. Measure the uneven shape. The minute signal amplifier operates to generate an output corresponding to the magnetic field on the sample surface based on the uneven shape of the sample, the displacement signal, and the reference signal.

  The magnetic force microscope of the present invention includes a cantilever having a tip made of a magnetic material or a tip coated with a thin film or formed of a magnetic material, and a first oscillator that excites the cantilever at a first resonance frequency of the cantilever. A displacement detector that detects the displacement of the tip of the cantilever, a fine movement element that fixes the sample on the upper surface, moves the probe closer to the sample, moves it away, or moves the measurement position, and a fine movement element A driving unit for driving, a second oscillator for exciting the sample at half the second resonance frequency of the cantilever, a displacement signal output from the displacement detector, and a reference signal that is the second resonance frequency And a small signal amplifier. Then, the driving unit drives the fine movement element based on the displacement of the tip of the cantilever detected by the displacement detector and the first resonance frequency, thereby moving the probe closer to or away from the sample. Measure the uneven shape. The second oscillator excites the sample to generate an external magnetic field that is greater than the coercivity of the magnetic material of the probe, and the micro signal amplifier is based on the concavo-convex shape of the sample, the displacement signal, and the reference signal. Operates to generate output in response to a magnetic field.

  The high spatial resolution magnetic field measurement method of the present invention excites a cantilever having a tip made of a magnetic material or a probe coated with a magnetic material or formed into a thin film with a first oscillator at the first resonance frequency of the cantilever. Measuring the concavo-convex shape of the sample by moving the probe toward or away from the sample based on the displacement of the tip of the cantilever and the first resonance frequency, and the second oscillator Exciting at the second resonance frequency, and generating an output corresponding to the magnetic field on the sample surface based on the measured uneven shape, the displacement of the tip of the cantilever, and the second resonance frequency.

  In the high spatial resolution magnetic field measuring method of the present invention, a cantilever having a tip made of a magnetic material or a tip coated with a magnetic material or formed into a thin film by a first oscillator at a first resonance frequency of the cantilever. Based on the excitation, the displacement of the tip of the cantilever and the first resonance frequency, the step of measuring the concavo-convex shape of the sample by moving the probe toward or away from the sample, and the second oscillator Exciting at a frequency half the second resonance frequency of the cantilever and generating an output corresponding to the magnetic field of the sample surface based on the measured uneven shape, displacement of the tip of the cantilever and the second resonance frequency; Have The second oscillator excites the sample to generate an external magnetic field greater than the coercive force of the magnetic material of the probe.

  Since magnetic field distribution data is acquired based on the second resonance frequency of the cantilever, the magnetic field distribution data with high resolution can be obtained without being affected by the phase fluctuation of the first resonance frequency and without incorporating a phase-locked loop. Can be obtained. Since the second resonance frequency of the cantilever used to excite the sample to be measured can be set to a frequency higher than the first resonance frequency, the measurement throughput can be increased and the measurement time can be shortened. Since the signal indicating the magnetic field distribution to be detected is not based on the FM signal but based on the second resonance frequency that is independent of the first resonance frequency, a signal can be obtained with a high S / N ratio.

  The second oscillator generates an external AC magnetic field that is equal to or greater than the coercive force of the magnetic material of the probe, and the magnetic field distribution that can be measured when the frequency twice the AC magnetic field is equal to the secondary resonance frequency of the cantilever. Spatial resolution can be increased.

It is a block diagram which shows the structural example of the magnetic force microscope of this invention. It is a figure which shows the relationship between the electric current sent through the exciting coil of the magnetic force microscope of this invention, and the output voltage of a displacement detection circuit. It is a figure (topography image) which shows the uneven | corrugated shape of the magnetic recording head measured with the magnetic force microscope of this invention. It is the figure which measured the magnitude | size of the magnetic field of the surface of the magnetic recording head of FIG. FIG. 5 is a diagram in which the magnetic field on the surface of the magnetic recording head of FIGS. FIG. 6 is a diagram obtained by three-dimensional data processing of the magnetic field data of FIG. 5. It is a figure which shows the measurement data of the magnitude | size of the magnetic field of the magnetic recording head surface measured with the magnetic force microscope of this invention for the comparison with a prior art. It is a figure which shows the measurement data of the magnitude | size of a magnetic field at the time of exciting the same thing as the magnetic recording head measured in FIG. 7 on the frequency of exactly 6 times the primary resonant frequency of a cantilever. It is a figure which shows the measurement result of the (a) Rcos (theta) component and (b) Rsin (theta) component of the magnetic field of a magnetic recording head measured by making the exciting current 1 mA _rms in the magnetic force microscope of this invention. In the magnetic force microscope which is a modification of the present invention, (a) the Rcos θ component and (a) when an external magnetic field exceeding the coercive force of the ferromagnetic probe is applied with an excitation current for exciting the sample to be measured being 5 mA _rms. b) It is a figure which shows the measurement result of Rsin (theta) component. In the magnetic force microscope which is a modified example of the present invention, (a) the R cos θ component when the excitation current for exciting the sample to be measured is 10 mA _rms and an external magnetic field exceeding the coercive force of the ferromagnetic probe is applied. b) It is a figure which shows the measurement result of Rsin (theta) component. In the magnetic force microscope which is a modified example of the present invention, (a) the R cos θ component when the exciting current for exciting the sample to be measured is 20 mA _rms and an external magnetic field exceeding the coercive force of the ferromagnetic probe is applied. b) It is a figure which shows the measurement result of Rsin (theta) component. It is a block diagram which shows the structure of the other modification of the magnetic force microscope of this invention. It is the topography image and magnetic field distribution image which were measured with the magnetic force microscope of the structure of FIG. (A) is a topography image when the exciting current is 1 mA _{rms in} order to generate a magnetic field less than the coercive force. (B) is a magnetic field distribution image under the conditions of (a). (C) is a topography image when the exciting current is 20 mA _{rms in} order to generate a magnetic field exceeding the coercive force. (D) is a magnetic field distribution image under the conditions of (c). It is a measurement result of a magnetic force microscope when the sample to be measured is excited beyond the coercive force with an alternating magnetic field having a frequency equal to the secondary resonance frequency of the cantilever for comparison of resolution. (A) shows magnetic field distribution. (B) shows an R cos θ image. (C) shows an Rsin θ image. (A) is a figure which shows the intensity distribution of the magnetic field in the cross section of the broken line of FIG.13 (d) as a voltage conversion value (cross-sectional profile). (B) is a diagram obtained by subjecting the cross-sectional profile data of (a) to Fourier transform in order to show the magnetic field distribution as a function of spatial frequency. FIG. 16 is a diagram illustrating data obtained by performing Fourier transform on profile data in the cross-sections of the broken lines in FIGS. 15A to 15C for comparison between the modified example and other modified examples.

[Configuration of magnetic force microscope]
FIG. 1 is a block diagram showing a configuration example of a magnetic force microscope of the present invention.

  A leaf spring (hereinafter also referred to as a cantilever) 2 to which a probe 1 having a ferromagnetic material at the tip is connected is fixed to the piezoelectric element 3 in a cantilever shape. The probe 1 is obtained by forming a CoCrPt alloy thin film on the surface of a silicon material. However, the magnetic material is not limited to CoCrPt, but may be other Co-based alloys such as CoCr alloy and CoPt alloy, and other magnetic materials such as ferrite, Fe, Ni, FePt, these alloys or permalloy, etc. There may be. The shape of the probe 1 is a cone or a pyramid. The cantilever 2 is made of silicon. However, the material is not limited to silicon but may be other materials such as silicon nitride. In general, the probe 1 and the cantilever 2 are formed by integral molding. However, in order to increase the resolution of the measurement, a silicon cantilever with a probe 1 made of carbon nanotubes may be added, or a needle-like magnetic material is grown on the tip of the integrally formed probe 1. There may be.

  The first oscillator 4 is connected to the piezoelectric element 3 on the fixed end side of the cantilever 2. The first oscillator 4 drives and vibrates the piezoelectric element 3 at a predetermined frequency, and vibrates the cantilever 2 at the primary resonance frequency. The first oscillator 4 is constituted by a function generator and generates a sine wave, but may be constituted by another sine wave generation circuit.

  An optical lever composed of a semiconductor laser 5, a light detection element 6 divided into four parts, and a displacement detection circuit 7 detects the laser light reflected by the cantilever 2 by the light detection element 6 in order to detect the vibration state of the cantilever 2. And photoelectric conversion. Then, the displacement detection circuit 7 detects changes in the amplitude and phase of the detected laser beam. The displacement detection of the cantilever 2 is not limited to the optical lever, and other methods using interference light, for example, a method using a focus error detection using an optical fiber interferometer or a prism, etc. can be used. A system other than the interference light, for example, a system using a magnetoresistive element or a system using a piezoelectric element can also be used.

  The output of the displacement detection circuit 7 is connected to the band-pass filter 9 and the RMS-DC converter 10 connected in series, and is connected to the z-axis drive unit 12 via the inverting input of the error amplifier 11. A standard reference voltage 11 a is connected to the non-inverting input of the error amplifier 11. The output of the error amplifier 11 is connected to the z-axis drive unit 12, and the output of the z-axis drive unit 12 is connected to the fine movement element 16 to drive the z scanner unit of the fine movement element 16. The z scanner unit is driven in the vertical direction by the z-axis drive unit 12 with respect to the measurement surface of the magnetic recording head 8 that is the sample to be measured.

  The signal processing control unit 17 is connected to the xy scanner unit and the coarse movement mechanism 20 of the fine movement element 16 via the xy scanning drive unit 18 and the coarse movement mechanism drive unit 19, respectively. The outputs of the z-axis driving unit 12 and the xy scanning driving unit 18 are further connected to a signal processing control unit 17, which performs signal processing as the uneven shape data of the sample to be measured, and monitors 22 as image data. Output to.

  A magnetic recording head 8 that is a sample to be measured is fixed to the upper surface of a fine movement element 16 that positions the sample to be measured in the order of nm in each direction of the xyz axis. The fine movement element 16 is fixed to the upper surface of the coarse movement mechanism 20 that positions and scans the sample to be measured in each direction of the xyz axis over a wide range. The fine movement element 16 and the coarse movement mechanism 20 control the distance and position between the tip of the probe 1 and the surface of the sample to be measured via the z-axis drive unit 12, the xy scanning drive unit 18, and the coarse movement mechanism drive unit 19. To do. Fine movement element 16 is formed of, for example, a piezoelectric element, and its displacement direction and displacement amount are controlled by a voltage applied by z-axis drive unit 12 or the like. On the other hand, the coarse movement mechanism controls the position of the measurement table by mechanical drive means, for example, motor control.

  The output of the second oscillator 13 is connected to the excitation coil 14 wound around the magnetic core of the magnetic recording head 8 that is the sample to be measured. The other terminal of the exciting coil 14 is grounded via the current limiting resistor 15. The output of the second oscillator 13 is connected to the reference input of the lock-in amplifier 21. The output of the optical lever displacement detection circuit 7 is connected to the lock-in amplifier 21. The lock-in amplifier 21 locks-in the output signal of the displacement detection circuit 7 based on the reference input signal that is the output of the second oscillator 13, and outputs the magnitude of the magnetic field and the phase data of the magnetic field. The output of the lock-in amplifier 21 is connected to the signal processing control unit 17, and the signal processing control unit 17 performs predetermined processing based on the input magnetic field magnitude and magnetic field phase data and monitors it as image data. 22 to output.

  Needless to say, the concavo-convex shape data and magnetic field distribution data subjected to signal processing in the signal processing control unit 17 can be output not only to the monitor 22 but also to other output devices such as a printer. Absent.

[Operation Principle of Magnetic Force Microscope of the Present Invention]
The cantilever 2 is a cantilever whose one end is a free end and has a plurality of resonance modes. In order to obtain the relationship between the primary resonance frequency f1 and the secondary resonance frequency f2, a dynamic equation of motion is considered for the vibration amplitude η in the deflection direction of the cantilever 2.

  Here, the cross-sectional area A, bending moment I, density ρ, and longitudinal elastic modulus E of the cantilever 2 are shown.

  When variable separation is performed with the vibration amplitude η (x, t) = Y (x) cos (ω · t + α), the equation (1) can be rewritten for Y (x) as follows.

  Thus, the general solution of Y (x) is as shown in the following formula (3).

  Here, considering the conditions of the fixed end and the free end, the boundary condition of the cantilever is expressed by the following equations (4) and (5).

  By substituting these boundary conditions into equation (2) and calculating, the following equation (6) is obtained.

  Here, the vibration equation representing the constraint condition of the vibration system is as the following expression (7).

  When m is obtained from Expression (7), m1 = 1.875104 and m2 = 4.694091, which correspond to the primary resonance frequency f1 and the secondary resonance frequency f2, respectively.

  Further, from the expression (2), the relationship between the angular frequency ω 1 and m can be expressed as follows.

From this, it can be seen that ω 1, that is, the resonance frequency f is proportional to the square of m. Therefore, the ratio between the primary resonance frequency f1 and the secondary resonance frequency f2 is f2 / f1 = (m2 / m1) ² = 6.266693. When the higher order m and ω are obtained by the same calculation, the ratio between the primary resonance frequency and the tertiary resonance frequency is about 17.5 times, and the ratio between the primary resonance frequency and the fourth resonance frequency is , About 33.4 times.

  The cantilever 2 has a plurality of unique resonance frequencies depending on its shape and material, and these resonance modes exist simultaneously in the same cantilever 2 without interfering with each other. Therefore, by adding a predetermined filter or the like, signals of these frequencies can be taken out independently. From this, in the magnetic force microscope of the present invention, for example, the excitation frequency is set to the secondary resonance frequency f2, and a configuration such as a filter for extracting the signal of the secondary resonance frequency f2 is added to the conventional magnetic force microscope. It becomes possible to directly output magnetic field data based on excitation signals. In this case, of course, it is not necessary to add a frequency modulation / demodulation function based on a specific frequency to the measurement system.

[Operation of magnetic force microscope]
Again, with reference to FIG. 1, operation | movement of the magnetic force microscope of this invention is demonstrated in detail.

  First, the uneven state measurement on the surface of the sample to be measured of the magnetic force microscope of the present invention is performed as follows.

  A cantilever 2 having a ferromagnetic probe 1 connected to the tip is fixed to a piezoelectric element 3 in a cantilever shape. As described above, the probe 1 is obtained by forming a CoCrPt alloy thin film on the surface of a silicon material, and the cantilever 2 is made of silicon. The cantilever 2 and the probe 1 are integrally molded. The piezoelectric element 3 is vibrated by the first oscillator 4, and the cantilever 2 is vibrated at the primary resonance frequency f1. Here, the primary resonance frequency f1 of the cantilever 2 is 58.306 kHz. As described above, since the secondary resonance frequency f2 is 6.266893 × f1, it is theoretically 365.397 kHz, but is 371.548 kHz in actual measurement. The reason why f2 / f1 = 6.37 is slightly different from the theoretical value is that the viscosity coefficient is different between the primary resonance frequency and the secondary resonance frequency. The first oscillator 4 is composed of a function generator. It goes without saying that the primary resonance frequency f1 of the cantilever can be arbitrarily set from the shape, material, etc. of the cantilever.

  An optical lever comprising a semiconductor laser 5, a light detection element 6 divided into four parts, and a displacement detection circuit 7 detects the vibration state of the cantilever 2. The signal detected by the displacement detection circuit 7 is input to the z-axis drive unit 12 by the error amplifier 11 via the bandpass filter 9 and the RMS-DC converter 10. Since the bandpass filter 9 and the RMS-DC converter 10 include a frequency component other than the primary resonance frequency f1 in the signal output from the optical lever displacement detection circuit 7, in order to remove these frequency components. Used for. The signal input to the error amplifier 11 is compared with the reference reference voltage 11a and input to the z-axis drive unit 12 as a signal negatively amplified by the error amplifier 11. When the z-axis drive unit 12 detects that the amplitude of the tip of the cantilever 2 is reduced by the negative feedback signal from the error amplifier 11, the z-scan unit of the fine movement element 16 is driven to move the magnetic recording head 8. Keep away from the probe 1. Conversely, when it is detected that the amplitude of the tip of the cantilever 2 has increased, the z scan portion of the fine movement element 16 is driven to bring the magnetic recording head 8 closer to the probe 1. The xy scanning unit of the fine movement element 16 drives the xy scanning driving unit 18 by the signal processing control unit 17 to move the measurement surface of the magnetic recording head 8 in a two-dimensional plane. In this way, a predetermined portion is scanned while keeping a predetermined distance from the surface shape of the magnetic recording head 8 which is a sample to be measured having unevenness, and the uneven shape on the surface of the magnetic recording head 8 is measured. The measured concavo-convex shape is obtained by inputting the drive signals of the z-axis drive unit 12 and the xy scanning drive unit to the signal processing control unit 17 and performing signal processing, thereby visualizing the concavo-convex shape (hereinafter also referred to as a topographic image). To the monitor 22.

  In the above description, the control for making the vibration amplitude at the tip of the cantilever 2 constant has been described. However, the uneven shape of the sample to be measured can also be controlled by detecting the displacement of the vibration phase and frequency and making these constant. Needless to say, it can be measured.

  Next, the magnetic force microscope of the present invention scans the probe 1 along the surface shape of the magnetic recording head 8 which is the sample to be measured, and the distance between the probe 1 and the magnetic recording head 8 is measured. The magnitude and phase of the magnetic field are measured while keeping the constant.

  The second oscillator 13 oscillates at the secondary resonance frequency f2 of the cantilever 2 and causes an alternating current to flow through the excitation coil 14, thereby exciting the magnetic recording head 8 that is the sample to be measured at the secondary resonance frequency f2. A signal detected by the optical lever displacement detection circuit 7 is input to the lock-in amplifier 21. The lock-in amplifier 21 locks-in the output signal of the displacement detection circuit 7 using the output signal of the second oscillator 13 as a reference signal. The lock-in detected signal is input to the signal processing control unit 17. The signal processing control unit 17 performs image processing on the lock-in detected signal, and outputs the magnetic field distribution and phase data on the surface of the magnetic recording head 8 to the monitor 22 for visualization. Thus, in the lock-in detection, the frequency of the reference signal is set to the secondary resonance frequency f2, so that even if the phase of the signal of the primary resonance frequency f1 fluctuates, the phase of the signal output from the lock-in amplifier 21 is changed. There is no impact.

  In the above description, the magnetic recording head 8 is excited by passing an exciting current through the exciting coil 14 wound around the magnetic core of the magnetic recording head 8 which is a sample to be measured, and the magnetic field distribution and phase on the surface are measured. . However, for example, when measuring the magnetic field distribution and phase on the surface of the magnetic recording medium of a hard disk, the magnetic recording medium is not accompanied by an exciting coil. Therefore, it is necessary to introduce a configuration for applying an external magnetic field to the sample to be measured into the measurement system. Therefore, a small coil for generating an external magnetic field is prepared separately from the magnetic recording medium that is the sample to be measured. For example, a loop coil in which a loop current path having a predetermined diameter and shape is patterned by using a well-known etching technique, which is obtained by pasting a Cu foil on a predetermined substrate. Instead of the exciting coil 14 of FIG. 1, a second oscillator 13 and a current limiting resistor 15 are connected to this loop coil. Then, this loop coil is arranged close to cover the magnetic recording medium to be measured, and the magnetic flux generated from the loop coil passes through the magnetic recording medium. By doing so, an external magnetic field can be applied to the magnetic recording medium by the excitation current flowing through the loop coil, and the surface magnetic field distribution of the magnetic recording medium can be measured by the same method as described above.

[Measurement result of magnetic force microscope]
The main magnetic pole portion of the magnetic recording head 8 was used as a sample to be measured. Measurement was performed by adjusting the current flowing through the exciting coil 14 so that the external magnetic field was less than the coercive force of the magnetic material of the probe 1. As shown in FIG. 2, the excitation current is adjusted so that the coercive force of the probe 1 is less than the coercive force. The excitation current flowing through the excitation coil 14 as an input and the output of the displacement detection circuit 7 as an output as an output This is because the voltage can maintain input / output linearity. It was confirmed that when the current flowing through the exciting coil 14 was 5 mA _rms or less, the magnetic material of the probe 1 was not magnetically saturated and the input / output linearity could be maintained.

  At the time of measurement, the surface of the sample to be measured was scanned at the main magnetic pole portion of the magnetic recording head 8 while keeping the vibration amplitude of the cantilever 2 constant, and a topography image was measured for one line at a speed of 1 Hz. Then, the same scanning line as the topographic image measurement was scanned to measure the magnetic field distribution. When measuring the magnetic field distribution, the vibration amplitude of the primary resonance frequency f1 is attenuated to 20% or less, and the height at which the concave and convex portions on the surface of the magnetic recording head 8 are traced is measured from the reference surface height to −24 nm. The measurement was performed close to

  When the second oscillator 13 oscillates at the secondary resonance frequency f2 (371.548 kHz) of the cantilever 2, an alternating current having the secondary resonance frequency f2 flows through the exciting coil 14. Then, an alternating magnetic field corresponding to the excitation current is generated from the main magnetic pole of the magnetic recording head 8, a magnetic force due to the interaction with the magnetic material of the probe 1 is applied to the probe 1, and the cantilever 2 has a secondary resonance frequency f2. Vibrate. The output of the displacement detection circuit 7 is input to the lock-in amplifier 21, and the reference input of the lock-in amplifier 21 is connected to the second oscillator 13. Then, the lock-in amplifier 21 locks-in the output signal of the displacement detection circuit 7 using the secondary resonance frequency f2 = 371.548 kHz as a reference frequency, and detects the Rcosθ component and the Rsinθ component that are magnetic field signals with phase information. Output. In order to improve the S / N ratio by adjusting the measurement range of the lock-in amplifier 21 to the maximum value of the detection signal, the time constant is set to 1 ms.

  With the above settings, the measurement of the topographic image with an image size of 256 pixels × 256 pixels and the magnetic field distribution with phase information could be completed in about 9 minutes. For comparison, when the conventional magnetic force microscope of Non-Patent Document 1-5 was used, the measurement time was about 40 minutes.

FIG. 3 to FIG. 6 show the results of measurement by flowing the secondary resonance frequency f2 = 371.548 kHz as the excitation frequency of the magnetic recording head 8 and 5 mA _rms as the excitation current through the excitation coil 14.

  FIG. 3 is a topography image measured with the magnetic force microscope having the above-described configuration. The main magnetic pole 30 is surrounded on three sides by the write shield part 31. The right side of the write shield part 31 is a side shield part 32.

  FIG. 4 is a diagram showing only the magnetic field magnitude distribution among the magnetic field distributions corresponding to the topographic image of FIG. It can be seen that the magnetic field in the vicinity of the main magnetic pole is strong and the magnetic field is weak in the write shield part 31.

  FIG. 5 is a diagram showing a magnetic force including phase information corresponding to the topographic image of FIG. 3, and shows that the direction of the magnetic field is opposite to that of the main magnetic pole in the side shield part 32. .

  FIG. 6 is a diagram obtained by performing the three-dimensional image processing on FIG. 5 and visually shows clearly which direction the direction of the magnetic field is relative to each part in addition to the magnitude of the magnetic field.

  As described above, in the magnetic force microscope of the present invention, it is easy to observe an alternating magnetic field image together with the uneven shape on the surface of the sample to be measured. In order to directly excite the cantilever 2 at a secondary resonance frequency of several hundred kHz or more, measurement can be performed in a shorter time than a conventional magnetic force microscope that measures from about 100 Hz to about 1 kHz. Further, as described in detail above, since frequency modulation is not used for measurement of the magnetic field distribution, it is not necessary to insert a phase-locked loop in the measurement system, and even if there is no phase-locked loop, a high S / It is possible to acquire magnetic field distribution data with an N ratio.

  7 to 8 show a magnetic force microscope of the present invention and a magnetic force microscope described in Patent Document 1 that excites a sample at a frequency that is not equal to the resonance frequency of the cantilever and is an integral multiple of the resonance frequency of the cantilever. The comparison of the measurement result with is shown.

  FIG. 7 is a measurement result of a magnetic field distribution with phase information by the magnetic force microscope of the present invention. The ratio between the primary resonance frequency f1 and the secondary resonance frequency f2 is about 6.3 times as described above. In this measurement, the primary resonance frequency f1 of the cantilever is 67.904 kHz, and the secondary resonance frequency f2 is 428.366 kHz. On the other hand, in FIG. 8, in order to obtain the measurement result using the magnetic force microscope described in Patent Document 1, the same sample cantilever (f1 = 67.904 kHz) is used as the sample to be measured in FIG. It is a measurement result when the exciting coil is excited with a current of 407.424 kHz, which is exactly six times the primary resonance frequency. The reason why the excitation frequency is set to 6 times the primary resonance frequency is that the frequency ratio in the magnetic force microscope of the present invention is an integer closest to 6.3 times.

  As is apparent from FIGS. 7 to 8, there is a great difference in the sharpness of the acquired image data. The signal that could be detected was 10 mV in the case of the magnetic force microscope of the present invention, whereas it was 300 μV in the conventional magnetic force microscope described in Patent Document 1. Therefore, the magnetic force microscope of the present invention can obtain a signal that is 33.3 times larger than that of the conventional magnetic force microscope described in Patent Document 1. From the above, the Q of the measurement system is increased by using the high-order resonance frequency unique to the cantilever rather than driving the sample to be measured by a simple harmonic of a frequency that is an integral multiple of the primary resonance frequency of the cantilever. A high S / N ratio can be realized by obtaining a high gain.

  In the above description, the resonance frequency used for the magnetic force measurement is the secondary resonance frequency. However, the resonance frequency is not limited to the secondary resonance frequency, and a tertiary or higher order resonance frequency may be used as the excitation frequency of the sample to be measured. However, the frequency ratio is about 17.5 times in the case of the third-order resonance frequency, and 34.4 times in the case of the fourth-order, which is a frequency of 1 MHz or more. It is necessary to pay attention to speed.

[Modification 1]
In the magnetic force microscope of the present invention, the alternating magnetic field generated from the sample to be measured is detected as the vibration of the cantilever 2 by the interaction with the ferromagnetic material of the probe 1. In the above-described embodiment, an external magnetic field having a magnitude that does not exceed the coercive force of the ferromagnetic material of the probe 1 is applied. In an external magnetic field less than the coercive force of the magnetic material of the probe 1, a signal having only the R cos θ component is detected in the magnetic field distribution, and R sin θ is almost zero. Here, when an external magnetic field exceeding the coercive force of the magnetic material of the probe 1 is used, the magnetization curve of the magnetic material has hysteresis, and as a result, not only Rcosθ but also the Rsinθ component can be detected. It becomes like this. By measuring the Rsin θ component, it becomes possible to clearly measure which part of the magnetic field is stronger than the R cos θ component alone.

FIG. 9 shows the measurement results of (a) R cos θ component and (b) R sin θ component when the exciting current of the exciting coil 14 is 1 mA _rms in order to obtain an external magnetic field equal to or less than the coercive force. The component shows almost no change, indicating that there is almost no Rsinθ component (zero). In order to increase the detection sensitivity of the magnetic field distribution, measurement was performed by bringing the probe 1 close to the surface of the sample to be measured up to a position of −34 nm of the reference plane height.

10 to 12, in order to apply an external magnetic field exceeding the coercive force of the probe 1 to the sample to be measured, the exciting current of the exciting coil 14 is 5 mA _rms in FIG. 10 and 10 mA _rms in FIG. 12 shows the measurement results of (a) R cos θ component and (b) R sin θ component when 20 mA _rms is set.

As shown in FIGS. 9A to 12A, the R cos θ component has almost no difference although the intensity is different. On the other hand, as shown in each figure (b), the Rsin θ component is detected as a signal is detected in the gap portion between the main magnetic pole 30 and the write shield part 31, the excitation current increases, and the external magnetic field increases. It can be seen that the intensity of the signal is also increased. Specifically, it can be seen that the main magnetic pole center region is becoming negative at 5 mA _rms , and that the entire main magnetic pole is negative at 10 mA _rms and 20 mA _rms . Further, at 10 mA _rms and 20 mA _rms , a magnetic distribution image reflecting the wedge shape of the main pole can be observed in the Rsin θ image.

  Thus, when the dynamic range of the measurement is insufficient with only the magnetic field distribution information of only the R cos θ component, the change of the R sin θ component is applied by applying an external magnetic field exceeding the coercive force of the probe 1. Thus, it is possible to obtain more detailed magnetic field distribution information.

  In addition, it is preferable to use the probe 1 used in the present modified example with a reduced outer dimension by controlling the surface covered with the magnetic material in order to improve the spatial resolution. For example, it is preferable that the tip of the probe 1 made of carbon nanotubes is coated with a magnetic material, or the tip of the probe 1 is crystal-grown with a needle-like magnetic material.

[Modification 2]
When an alternating magnetic field exceeding the coercive force of the probe connected to the tip of the cantilever is applied, an attractive force acts on the cantilever every time the magnetic field exceeds the coercive force of the ferromagnetic material constituting the probe. This indicates that an attractive force is generated between the cantilever and the sample to be measured at a frequency twice the frequency of the applied AC magnetic field. Therefore, the magnetic force can be measured in the attractive mode having a frequency equal to the secondary resonance frequency by exciting the sample to be measured at half the secondary resonance frequency.

  FIG. 13 is a block diagram illustrating a configuration example of a magnetic force microscope according to another modification of the present invention. Compared to the configuration of Modification 1 described above, the frequency of the alternating magnetic field applied to the sample to be measured is different from that of the secondary resonance frequency f2 of the cantilever 2.

  Similar to the case shown in FIG. 1 described above, a cantilever 2 to which a probe 1 having a ferromagnetic material at the tip is connected is fixed to a piezoelectric element 3 in a cantilever shape. The probe 1 is obtained by forming a CoCrPt alloy thin film on the surface of a silicon material. The magnetic material is not limited to CoCrPt, and may be other Co-based alloys such as CoCr alloy and CoPt alloy, and other magnetic materials such as ferrite, Fe, Ni, FePt, alloys thereof, permalloy, etc. This is also the same as in the case of FIG. For example, PPP-MFMR manufactured by Nanoworld may be used, and the coercive force in this case is about 300 Oe.

  The first oscillator 4 is connected to the piezoelectric element 3 on the fixed end side of the cantilever 2. The first oscillator 4 drives the piezoelectric element 3 to vibrate the cantilever 2 at the primary resonance frequency.

  An optical lever composed of a semiconductor laser 5, a light detection element 6 divided into four parts, and a displacement detection circuit 7 detects the laser light reflected by the cantilever 2 by the light detection element 6 in order to detect the vibration state of the cantilever 2. And photoelectric conversion. Then, the displacement detection circuit 7 detects changes in the amplitude and phase of the detected laser beam. As in the case of FIG. 1, the detection of the displacement of the cantilever 2 is not limited to an optical lever, but a method using other interference light, for example, a method using focus error detection using an optical fiber interferometer or a prism. Further, a method other than the interference light, for example, a method using a magnetoresistive element or a method using a piezoelectric element can be used.

  The output of the displacement detection circuit 7 is connected to the band-pass filter 9 and the RMS-DC converter 10 connected in series, and is connected to the z-axis drive unit 12 via the inverting input of the error amplifier 11. A standard reference voltage 11 a is connected to the non-inverting input of the error amplifier 11. The output of the error amplifier 11 is connected to the z-axis drive unit 12, and the output of the z-axis drive unit 12 is connected to the fine movement element 16 to drive the z scanner unit of the fine movement element 16. The z scanner unit is driven in the vertical direction by the z-axis drive unit 12 with respect to the measurement surface of the magnetic recording head 8 that is the sample to be measured.

  The signal processing control unit 17 is connected to the xy scanner unit and the coarse movement mechanism 20 of the fine movement element 16 via the xy scanning drive unit 18 and the coarse movement mechanism drive unit 19, respectively. The outputs of the z-axis driving unit 12 and the xy scanning driving unit 18 are further connected to a signal processing control unit 17, which performs signal processing as the uneven shape data of the sample to be measured, and monitors 22 as image data. Output to.

  A magnetic recording head 8 that is a sample to be measured is fixed to the upper surface of a fine movement element 16 that positions the sample to be measured in the order of nm in each direction of the xyz axis. The fine movement element 16 is fixed to the upper surface of the coarse movement mechanism 20 that positions and scans the sample to be measured in each direction of the xyz axis over a wide range. The fine movement element 16 and the coarse movement mechanism 20 control the distance and position between the tip of the probe 1 and the surface of the sample to be measured via the z-axis drive unit 12, the xy scanning drive unit 18, and the coarse movement mechanism drive unit 19. To do. Fine movement element 16 is formed of, for example, a piezoelectric element, and its displacement direction and displacement amount are controlled by a voltage applied by z-axis drive unit 12 or the like. On the other hand, the coarse movement mechanism controls the position of the measurement table by mechanical drive means, for example, motor control.

  The second oscillator 13a outputs a half frequency of the secondary resonance frequency f2 of the cantilever 2. The output of the second oscillator 13a is connected to the excitation coil 14 wound around the magnetic core of the magnetic recording head 8 that is the sample to be measured. The other terminal of the exciting coil 14 is grounded via the current limiting resistor 15.

  The third oscillator 13b outputs the frequency of the secondary resonance frequency f2 of the cantilever 2. The output of the third oscillator 13b is connected to the reference input of the lock-in amplifier 21. The output of the optical lever displacement detection circuit 7 is connected to the lock-in amplifier 21. The lock-in amplifier 21 performs lock-in detection on the output signal of the displacement detection circuit 7 based on the reference input signal that is the output of the second oscillator 13a, and outputs the magnetic field magnitude and magnetic field phase data. The output of the lock-in amplifier 21 is connected to the signal processing control unit 17, and the signal processing control unit 17 performs predetermined processing based on the input magnetic field magnitude and magnetic field phase data and monitors it as image data. 22 to output.

  Note that a signal having a frequency equal to the secondary resonance frequency of the cantilever 2 may be input as a reference frequency of the lock-in amplifier 21 through a multiplier that doubles the output of the second oscillator 13a. Alternatively, a signal of the secondary resonance frequency f2 input to the lock-in amplifier 21 as a reference frequency and having a frequency of (1/2) f2 by a frequency divider may be used for exciting the sample to be measured.

  14 to 17 show the results measured with the configuration of FIG. As specific measurement conditions, the cantilever 2 is excited in the range of the primary resonance frequency f1 to 67.481 kHz, and a topography image is measured in the same manner as in FIG. Here, for example, the vibration amplitude of the cantilever 2 is set to 0.5 Vpp.

  Next, in order to acquire the magnetic field distribution, the distance between the probe 1 and the magnetic recording head 8 is controlled so as to keep the vibration amplitude of the cantilever 2 constant in the main magnetic pole portion of the magnetic recording head 8 that is the sample to be measured. Scan while. Here, for example, the vibration amplitude of the cantilever 2 is lowered to 0.1 Vpp to bring the position of the vibration center closer to the distance of 8 nm from the sample surface. Since the secondary resonance frequency f2 of the cantilever 2 in this case is 424.324 kHz, the frequency for exciting the magnetic recording head 8 is 221.162 kHz, which is a half of this frequency.

  In this way, the magnetic field distribution image is measured using the lock-in amplifier 21 by using the optical lever with the secondary resonance frequency f2 of the cantilever 2 as the frequency of the reference input signal.

  For example, while controlling the distance between the probe 1 and the sample to be measured, scanning is performed at 1 Hz per line, and the surface shape is measured and stored. Then, a magnetic field distribution image is measured while maintaining a certain distance from the surface along the stored surface shape. Then, as in the case of FIG. 1 and the like described above, the measurement time of the topographic image and magnetic field distribution image of 256 pixels × 256 pixels is about 9 minutes.

As shown in FIGS. 14A and 14C, the same topographic image is obtained even if the excitation current is 1 mA _rms less than the coercive force of the ferromagnetic material of the probe 1 or 20 mA _rms exceeding the coercive force. can do. On the other hand, as shown in FIG. 14B, when the exciting current is 1 mA _rms below the coercive force, almost nothing is detected as the magnetic field distribution image. As shown in FIG. _14D , when the excitation current is 20 mA _rms , the shape of the tip of the wedge-shaped head can be confirmed as a magnetic field distribution image.

  In order to confirm the spatial resolution, a magnetic field distribution image obtained by applying the AC magnetic field exceeding the coercive force to the sample to be measured and measuring the frequency of the AC magnetic field again at a frequency equal to the secondary resonance frequency f2 in order to confirm the spatial resolution. What was acquired is shown to Fig.15 (a)-(c). As described in the first modification, the Rsin θ image can be measured including the magnetic field generation direction.

FIG. 16A is a diagram showing a cross-sectional profile of the broken line in FIG. 14D, which is proportional to the strength of the magnetic field, with the lower side of FIG. 14D being the distance reference (x = 0 nm). The voltage is plotted. Near the center (x = 530 nm), the magnetic field strength is increased by the magnetic pole. Data as shown in FIG. 16B is obtained by Fourier transforming the cross-sectional profile of FIG. From the Fourier transform data, it can be seen that the signal intensity is substantially constant at −37 dB at the spatial frequency kx = 95 μm ⁻¹ or more. Here, the signal strength −37 dB is thermal noise that does not depend on the spatial frequency. On the other hand, since the spatial frequency kx = 95 μm ⁻¹ or less has a signal intensity greater than that of the thermal noise, the spatial frequency kx = 95 μm ⁻¹ is the maximum spatial frequency that can be detected without being buried in the thermal noise. Correspond. Accordingly, the minimum spatial resolution can be estimated by taking the reciprocal of this maximum spatial frequency, and the minimum value of the spatial resolution in the case of FIG. 16B can be 10.52 nm.

  The above is the spatial resolution when the sample to be measured is excited at a frequency half that of the secondary resonance frequency f2 of the cantilever 2, but the spatial resolution when the sample to be measured is excited at the secondary resonance frequency f2 of the cantilever 2 is also described. 15A to 15C can be similarly estimated from the cross-sectional profile of the broken line in FIGS. FIGS. 17A to 17C are diagrams obtained by Fourier transforming the cross-sectional profiles corresponding to FIGS. 15A to 15C, respectively. The minimum value of the spatial resolution obtained from the maximum value of the spatial frequency that is not buried in the thermal noise of the measurement system is 20.41 nm for R cos θ from FIG. Further, from FIG. 17C, Rsinθ is 17.85 nm.

  When the sample to be measured is excited beyond the coercive force of the ferromagnetic probe, by exciting at a frequency half that of the secondary resonance frequency f2 of the cantilever, excitation is performed at the secondary resonance frequency f2. Magnetic field distribution images can be measured with a spatial resolution of about twice.

  In the above description, the excitation frequency of the cantilever 2 is the primary resonance frequency of the cantilever 2, and the excitation frequency of the sample to be measured is ½ the secondary resonance frequency of the cantilever 2. By securing the above, higher order resonance frequencies may be used. For example, the excitation frequency of the cantilever 2 can be the secondary resonance frequency, and the excitation frequency of the sample to be measured can be the tertiary resonance frequency. Alternatively, the excitation frequency of the cantilever 2 may be kept at the primary resonance frequency, and the excitation frequency of the sample to be measured may be half the resonance frequency of the third or higher order.

  As in the case of the configuration example of FIG. 1, a loop coil may be used instead of the excitation coil 14 wound around the magnetic core of the magnetic recording head 8 that is the sample to be measured. The loop coil can be formed, for example, by patterning a loop current path having a predetermined diameter and shape using a well-known etching technique with a Cu foil pasted on a predetermined substrate. The second oscillator 13a and the current limiting resistor 15 are connected to the loop coil, and the loop coil is disposed in close proximity so as to cover the magnetic recording medium to be measured, so that the magnetic flux generated from the loop coil is a magnetic recording medium. To pass through. By doing so, an external magnetic field can be applied to the magnetic recording medium by the excitation current flowing through the loop coil, and the surface magnetic field distribution of the magnetic recording medium can be measured by the same method as described above.

  The magnetic force microscope described above is for explaining a specific example, and is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention. Needless to say.

  1 probe, 2 cantilever, 3 piezoelectric element, 4 first oscillator, 5 laser, 6 light receiving element, 7 displacement detector, 8 magnetic recording head, 9 bandpass filter, 10 RMS-DC converter, 11 error amplifier, 11a reference reference voltage, 12 z-axis drive unit, 13, 13a second oscillator, 13b third oscillator, 14 exciting coil, 15 current limiting resistor, 16 fine movement element, 17 signal processing control unit, 18 xy scanning drive unit, 19 Coarse mechanism drive unit, 20 Coarse mechanism, 21 Lock-in amplifier, 22 Monitor, 30 Main pole, 31 Write shield, 32 Side shield

Claims (14)

A cantilever having a tip made of a magnetic material or a tip coated with a magnetic material or formed into a thin film at the tip;
A first oscillator for exciting the cantilever at a first resonance frequency of the cantilever;
A displacement detector for detecting the displacement of the tip of the cantilever;
A fine movement element that fixes the sample on the upper surface and moves the probe closer to, away from, or moving the measurement position;
A drive unit for driving the fine movement element;
A second oscillator for exciting the sample at a second resonance frequency of the cantilever;
A minute signal amplifier for inputting a displacement signal output from the displacement detector and a reference signal having the second resonance frequency;
The drive unit drives the fine movement element based on the displacement of the tip of the cantilever detected by the displacement detector and the first resonance frequency, thereby causing the probe to approach the sample or Separate and measure the uneven shape of the sample,
The magnetic signal microscope characterized in that the minute signal amplifier generates an output corresponding to the magnetic field on the sample surface based on the uneven shape of the sample, the displacement signal, and the reference signal. The first resonance frequency is a primary resonance frequency of the cantilever,
The magnetic force microscope according to claim 1, wherein the second resonance frequency is a secondary or higher order resonance frequency of the cantilever.   The magnetic force microscope according to claim 2, wherein the high-order resonance frequency is a secondary resonance frequency. The displacement detector is
A laser output unit for outputting laser light;
A light receiving element that receives the reflected light reflected by the cantilever of the laser light output from the laser output unit;
The magnetic force microscope according to claim 1, wherein the magnetic force microscope includes an optical lever including a signal processing unit that measures an amount of displacement of the cantilever by processing an electric signal converted by the light receiving element.   2. The magnetic force microscope according to claim 1, wherein the second oscillator excites the sample at the second resonance frequency via a coil disposed close to the sample so as to cover the sample.   2. The magnetic force microscope according to claim 1, wherein the minute signal amplifier is a lock-in amplifier.   The magnetic force microscope according to claim 1, wherein the second oscillator excites the sample to generate an external magnetic field greater than the coercive force of the magnetic material of the probe. A cantilever having a tip made of a magnetic material or a tip coated with a magnetic material or formed into a thin film at the tip;
A first oscillator for exciting the cantilever at a first resonance frequency of the cantilever;
A displacement detector for detecting the displacement of the tip of the cantilever;
A fine movement element that fixes the sample on the upper surface and moves the probe closer to, away from, or moving the measurement position;
A drive unit for driving the fine movement element;
A second oscillator for exciting the sample at half the second resonant frequency of the cantilever;
A minute signal amplifier for inputting a displacement signal output from the displacement detector and a reference signal having the second resonance frequency;
The drive unit drives the fine movement element based on the displacement of the tip of the cantilever detected by the displacement detector and the first resonance frequency, thereby causing the probe to approach the sample or Separate and measure the uneven shape of the sample,
The second oscillator excites the sample to generate an external magnetic field greater than the coercive force of the magnetic material of the probe,
The magnetic signal microscope characterized in that the minute signal amplifier generates an output corresponding to the magnetic field on the sample surface based on the uneven shape of the sample, the displacement signal, and the reference signal. The first resonance frequency is a primary resonance frequency of the cantilever,
The magnetic force microscope according to claim 8, wherein the second resonance frequency is a secondary or higher order resonance frequency of the cantilever.   The magnetic force microscope according to claim 9, wherein the high-order resonance frequency is a secondary resonance frequency. The first oscillator excites a cantilever having a tip made of a magnetic material or a tip coated with a magnetic material or formed into a thin film at a tip at the first resonance frequency of the cantilever, and the displacement of the tip of the cantilever and the first Measuring the concavo-convex shape of the sample by moving the probe closer to or away from the sample based on the resonance frequency of
The sample is excited by the second oscillator at the second resonance frequency of the cantilever, and the magnetic field on the surface of the sample is determined based on the measured uneven shape, the displacement of the tip of the cantilever and the second resonance frequency. Generating a responsive output. A high spatial resolution magnetic field measurement method. The first resonance frequency is a primary resonance frequency of the cantilever,
The high spatial resolution magnetic field measurement method according to claim 11, wherein the second resonance frequency is a second or higher order resonance frequency of the cantilever.   The high spatial resolution magnetic field measurement method according to claim 12, wherein the high-order resonance frequency is a secondary resonance frequency of the cantilever. The first oscillator excites a cantilever having a tip made of a magnetic material or a tip coated with a magnetic material or formed into a thin film at a tip at the first resonance frequency of the cantilever, and the displacement of the tip of the cantilever and the first Measuring the concavo-convex shape of the sample by moving the probe closer to or away from the sample based on the resonance frequency of
The sample is excited by a second oscillator at half the frequency of the second resonance frequency of the cantilever, and based on the measured uneven shape, the displacement of the tip of the cantilever and the second resonance frequency, Generating an output corresponding to the magnetic field of the sample surface,
The method of measuring a high spatial resolution magnetic field, wherein the second oscillator excites the sample to generate an external magnetic field greater than the coercive force of the magnetic material of the probe.