JP2004279099A - External magnetic field sweep magnetic force microscope and measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic force microscope capable of performing quantitative magnetic measurement at a local spot by a new-generation magnetic application element having high density, and knowing a dynamic characteristic by an external magnetic field at the local spot, without requiring an operator to do troublesome works for setting operation, data collection, and data processing analysis. <P>SOLUTION: This magnetic force microscope is equipped with a cantilever having a micro-probe equipped with a greater coercive force on the tip than the maximum external magnetic field, a means for detecting displacement of the cantilever, a means for vibrating the distance between the cantilever and a sample in a fixed cycle with a desired amplitude quantity. a moving means for moving the sample relatively to the probe, an external magnetic field device comprising an electromagnet capable of applying a magnetic field perpendicular or in parallel to the sample, a means for sweeping the direction and the magnitude of the magnetic field, and a synchronous amplifier for outputting an MFM signal synchronously with the external magnetic field. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetic force microscope capable of measuring a local magnetization of a sample, and more particularly to a technique suitable for inspecting magnetic characteristics of a magnetic application element such as a miniaturized magnetic recording medium.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, magnetization measurement of a magnetic material has been performed exclusively using a vibrating sample magnetometer (VSM) or the like. This VSM is based on S.M. Forner, and its basic configuration is shown in Non-Patent Document 1. As shown in FIG. 5, the sample is attached to the tip of the output rod of the vibrator, and an electromagnet for generating a magnetic field for the sample and a sensor coil for detecting the magnetic field near the sample are arranged, and the output end of the sensor coil is locked in. This is connected to the input terminal of the amplifier. A sample is excited at a constant frequency by a vibrator in a magnetic field generated by an electromagnet, and at that time, an AC electromotive force induced in a sensor coil is detected via a lock-in amplifier synchronized with the frequency. However, this sample vibration type magnetometer measures the magnetism near the sample using a coil, and is a macro-measurement. The magnetization could not be measured locally.
[0003]
Therefore, recently, a magnetic force microscope (MFM: Magnetic Force Microscope) which is a kind of a probe microscope detects a magnetic force (attractive force / repulsive force) applied between the sample and the tip of the probe to measure a local magnetic state of the sample. Attempts have been made to do so. The ultra-small magnetic domain observation device disclosed in Patent Document 1 is designed to enable observation of a change in a magnetic domain due to application of a magnetic field by a magnetic force microscope without performing a complicated positioning procedure of an observation point. As shown in FIG. 4, as shown in FIG. 4, an arrangement portion of an extremely small magnetic domain observation sample, a probe 1 of a magnetic force microscope arranged to face the sample surface, and An external magnetic field applying means 6 for applying an external magnetic field is provided, and observation of a very small magnetic domain on a sample surface is performed based on the principle of a magnetic force microscope. According to this device, the direction and magnitude of the magnetic field applied to the sample can be changed as appropriate, so that, for example, a dynamic observation of a magnetic domain generation state and a magnetization reversal state can be performed. It is described in the specification that changes before and after the application of a magnetic field to a sample can be statically observed.
By the way, in next-generation magnetic application elements such as patterned media, MRAM, and spin transistors, there is a need to quantitatively measure magnetization at a locally formed pattern. Also in the development of magnetic recording media, it is necessary to know the dynamic characteristics of a local external magnetic field. However, when measuring the characteristics of such a sample using the apparatus disclosed in Patent Document 1, the operator must perform the measurement while manually adjusting the magnetic field generated by the magnetic field applying unit as appropriate, and the data collection is also performed. Data processing and analysis can be a daunting task.
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 9-218213, "Micro-microdomain observation method and micro-microdomain observation apparatus" Published on August 19, 1997 [Non-Patent Document 1]
http: // mswebs. aist-nara. ac. jp / LABs / sharp / vsm. html
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide an operator with a quantitative measurement of local magnetization of a next-generation magnetic application element with high density without troublesome setting operation and data collection and troublesome processing and analysis of the data. Another object of the present invention is to provide a magnetic force microscope capable of knowing dynamic characteristics of a local external magnetic field.
[0006]
[Means for Solving the Problems]
The magnetic force microscope according to the present invention includes a cantilever having a minute probe having a coercive force larger than the maximum external magnetic field at the tip, a means for detecting displacement of the cantilever, and a desired distance between the cantilever and the sample at a constant period. Means for vibrating with the amplitude, moving means for moving the sample relative to the probe, an external magnetic field device comprising an electromagnet capable of applying a magnetic field perpendicularly or parallel to the sample, and adjusting the direction and magnitude of the magnetic field A sweeping means and a synchronous amplifier for outputting an MFM signal in synchronization with an external magnetic field are provided.
A means for driving and scanning the probe from a predetermined position to another predetermined position so that dynamic characteristics can be more easily measured; a means for calculating a difference between MFM signals of a magnetic portion and a non-magnetic portion of the sample; A means for sweeping an external magnetic field over a predetermined inverted value from a value and a means for storing the value of the MFM signal difference corresponding to the external magnetic field value are provided.
[0007]
The magnetic force microscope of the present invention has a function of compensating and removing the characteristic component inherent in the apparatus. Therefore, means for sweeping an external magnetic field from a predetermined value to a predetermined reversal value, and a response MFM from a probe set at a fixed point of a standard sample Means are provided for storing the signal in association with the external magnetic field value, and means for calculating the difference between the stored value corresponding to the same external magnetic field value from the detected MFM signal.
Further, the magnetic force microscope of the present invention includes a means for changing the external magnetic field into a pulse having a sharp rise and a sharp fall so as to measure the switching characteristics of the sample locally, and a probe installed at a predetermined position of the sample. A means for storing the response MFM signal from the needle together with the elapsed time and a means for displaying the external magnetic field and the MFM signal on the time axis are provided.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention has been developed for inspecting the magnetic characteristics of a magnetic application element such as a magnetic recording medium that has been miniaturized as described above. In consideration of detecting the magnetic characteristics of an extremely small area, the sensor has been sharpened. It is conceived to use a magnetic force microscope which is a kind of a probe microscope for detecting a magnetic force acting between a probe tip and a sample surface facing the same. The basic configuration of the magnetic force microscope device is the same as that of a conventional device such as Patent Document 1. That is, as shown in FIG. 1, a cantilever 2 having a minute probe 1 having a magnetic material disposed at a tip thereof, a means 3 for detecting the displacement of the cantilever 2, and the cantilever 2 being fixed to the surface of the sample 10 at regular intervals. Exciting means 4 such as a piezo material which vibrates at a desired amplitude, moving means 5 for moving the sample 10 relatively to the probe 1, and an electromagnet or the like which can apply a magnetic field perpendicularly or parallel to the sample 10. External magnetic field applying means 6. In the magnetic force microscope of the present invention, the value of the magnetic field generated by the conventional external magnetic field applying means 6 is not appropriately set by the operator, but is swept so as to continuously change from a predetermined value set by the operator to a predetermined value. It is characterized in that a synchronous amplifier 7 for outputting an MFM signal in synchronization with the change of the external magnetic field is provided. The external magnetic field is automatically swept as set, and the MFM detection signal at that time is taken out through the synchronous amplifier 7 that outputs the MFM signal in synchronization with the change of the external magnetic field. The signal can be obtained directly. For sweeping from a predetermined value to a predetermined value, the setting may be registered in the computer 8 and the computer 8 transmits a sweep drive signal to the external magnetic field applying means 6 and also sends it to the synchronous amplifier 7 as a synchronous signal during operation. The sweep signal can be changed over a range in which the polarity of the magnetic field is reversed.
[0009]
Embodiment 1
Next, an embodiment of the present invention suitable for measuring the magnetization hysteresis characteristic of a specific minute region will be described. The magnetic force microscope apparatus of this embodiment includes a means for repeatedly driving and scanning the probe from a predetermined position on the sample surface to another predetermined position in addition to the above-described basic configuration of the present invention, and a magnetic part and a non-magnetic part of the sample. , A means for sweeping an external magnetic field from a predetermined value to an inverted predetermined value, and a means for storing the value of the MFM signal difference corresponding to the external magnetic field value.
The means for driving and scanning the probe from a predetermined position on the sample surface to another predetermined position is, for example, a means for transmitting a drive signal to the moving means 5 so that the probe 1 performs linear scanning repeatedly between two points. Move the tip relatively. In the illustrated example, the sample stage 9 on which the sample 10 is placed is repeatedly moved in one direction by a predetermined distance. For example, if a magnetic chip and a non-magnetic part are arranged alternately in a memory chip in which a sample is densified, when the probe 1 is scanned in one direction on the surface of the sample, the probe 1 crosses the magnetic region and the non-magnetic region, and the MFM signal outputs both values alternately. As shown in FIG. 2, assuming that the scanning range of the sample surface is two magnetic portions (white regions) and two non-magnetic regions (speckled regions), it depends on which region the triangular probe 1 faces. The MFM signal changes in a rectangular manner. The signal in the non-magnetic region does not change according to the value of the external magnetic field, but the signal in the magnetic region changes. In addition, when the polarity of the external magnetic field is reversed, the MFM signal is also positive or negative, that is, the force applied between the sample surface and the probe is reversed from the attractive force to the repulsive force. However, it is necessary that the coercive force of the probe take a sufficiently large value so as not to be reversed by the maximum external magnetic field.
[0010]
Next, means for calculating and storing the difference between the MFM signals of the magnetic portion and the non-magnetic portion of the sample will be described. In this embodiment, when the value H of the external magnetic field is swept as if it changes in the range of ± K, the frequency is repeated a plurality of times while the probe 1 passes through one region of the magnetic portion and the non-magnetic portion. Will be. When the probe 1 faces the magnetic part, the MFM signal changes beyond positive and negative in response to a change in the external magnetic field. On the other hand, when the probe 1 faces the non-magnetic portion, the MFM signal keeps 0 value regardless of the change of the external magnetic field. In the present invention, the MFM signal is taken out in synchronization with the external magnetic field sweep signal via the synchronous amplifier 7, so that the MFM signal of the magnetic part and the MFM signal of the non-magnetic part under the same external magnetic field can be easily matched. it can. Further, the difference between the values can be stored in the storage means of the computer. This is the means for calculating and storing the difference between the MFM signals of the magnetic part and the non-magnetic part of the sample of the present embodiment. Based on accumulated information of the difference calculation value in one probe scan or a plurality of scans, for example, the intensity of the external magnetic field is plotted on the horizontal axis and the corresponding MFM signal value is plotted on the vertical axis, and displayed on the display 11. Then, the magnetization hysteresis characteristic of a specific portion of the sample as shown in the center of FIG. 2 can be directly displayed in a graph. In order to obtain this characteristic with a conventional magnetic force microscope, the probe is scanned while the external magnetic field is set to a predetermined value, and the MFM signals of the magnetic part and the non-magnetic part of the sample are stored. A task of storing a similar MFM signal with a slight change is repeated in correspondence with all external magnetic fields, and the troublesome task of organizing the acquired data and displaying the data in a graph is required. In this apparatus, calibration of magnetization measurement can be performed by measurement using a standard sample such as VSM.
The sample of this device is not limited to a memory chip having a magnetic portion and a non-magnetic portion arranged, but even a uniform magnetic member can be obtained by placing a dummy of non-magnetic material next to the sample. It can be measured using an apparatus.
[0011]
Embodiment 2
An embodiment of the present invention having a function of compensating and removing the characteristic component unique to the device will be described. The apparatus of this embodiment has, in addition to the basic configuration of the present invention described above, means for sweeping an external magnetic field from a predetermined value to an inverted predetermined value, and a response MFM signal from a probe set at a fixed point of a standard sample to an external magnetic field value. Means for storing the values in association with each other, and means for calculating the difference between the stored values corresponding to the same external magnetic field value from the detected MFM signal. A non-magnetic material is generally used for the standard sample, and the probe 1 is made to face the fixed point, and an external magnetic field is swept to acquire an MFM signal. Since the sample is a non-magnetic material, the MFM signal should have a value of 0 regardless of the value of the external magnetic field. However, noise may be superimposed on the signal depending on conditions such as the structure of the device itself. Therefore, if the MFM signal is acquired by sweeping the external magnetic field with respect to the non-magnetic sample using the apparatus of the present embodiment, the MFM signal can be obtained as noise itself. When this value is stored and the actual sample is measured, subtracting this value from the obtained MFM signal makes it possible to compensate and remove the characteristic characteristic of the apparatus.
[0012]
Embodiment 3
Next, a description will be given of an embodiment of the present invention capable of measuring a switching characteristic at a local portion of a sample. The apparatus of this embodiment has, in addition to the basic configuration of the present invention described above, means for changing the external magnetic field into a pulse having a steep rising and a steep falling, and a response MFM signal from a probe installed at a predetermined position of the sample. An external magnetic field sweeping magnetic force microscope comprising means for storing the elapsed time and an external magnetic field and a means for displaying the MFM signal along the time axis. The means for changing the external magnetic field into a pulse having a steep rise and a steep fall is provided by the external magnetic field applying means 6 as shown in FIG. The intensity acts to rise sharply from the value a to the value b, and to fall sharply from the value b to the value a after a certain time. This can be realized by setting the a value and the b value in the computer 8 so as to send the control signal from the computer 8 to the external magnetic field applying means 6. An MFM signal responding to this pulse-like magnetic field change is extracted and displayed on the display 11 with the time axis aligned. Then, the rising characteristics and the falling characteristics of the MFM signal are shown as they are. From this response characteristic, the switching characteristic of the material at a specific position of the sample to which the probe 1 is fixed can be grasped at a glance. This device can measure, for example, the storage speed of a magnetic memory.
【The invention's effect】
[0013]
An external magnetic field sweeping magnetic force microscope according to the present invention includes a cantilever having a minute probe having a coercive force larger than the maximum external magnetic field at the tip, a unit for detecting displacement of the cantilever, and a distance between the cantilever and the sample surface which is constant. Excitation means for oscillating at a desired amplitude amount, moving means for moving the sample relative to the probe, external magnetic field applying means comprising an electromagnet capable of applying a magnetic field perpendicular or parallel to the sample, and external magnetic field And a synchronous amplifier that outputs an MFM signal in synchronization with the external magnetic field. Therefore, the MFM signal is detected in synchronization with the external magnetic field while sweeping the external magnetic field, and the local magnetization of the sample is detected. The measurement can be easily performed without requiring the troublesome work of the operator.
A means for driving and scanning the probe from a predetermined position to another predetermined position; a means for calculating a difference between MFM signals of a magnetic portion and a non-magnetic portion of the sample; and a sweeping of an external magnetic field from a predetermined value to an inverted predetermined value. And further comprising means for storing the value of the MFM signal difference corresponding to the external magnetic field value, so that the magnetization characteristics in the local part of the sample can be easily measured without requiring a troublesome operation of the operator. . Based on the accumulated information, for example, plotting the strength of the external magnetic field on the horizontal axis and the corresponding MFM signal value on the vertical axis and displaying the plotted value on the display 12, the sample shown in the center of FIG. The magnetization hysteresis characteristics of the portion can be directly displayed on a graph.
[0014]
The external magnetic field sweeping magnetic force microscope of the present invention is a means for sweeping an external magnetic field from a predetermined value to an inverted predetermined value, and stores a response MFM signal from a probe set at a fixed point of a standard sample in association with the external magnetic field value. Means, and a means for calculating the difference between the stored values corresponding to the same external magnetic field value from the detected MFM signal, thereby providing a function of compensating and removing a characteristic component unique to the device during normal MFM operation. .
A means for changing the external magnetic field into a pulse having a sharp rise and a sharp fall; a means for storing a response MFM signal from a probe installed at a predetermined position of the sample along with an elapsed time; and a means for storing the external magnetic field and the MFM signal. The external magnetic field sweeping magnetic force microscope according to the present invention, further comprising means for displaying the images in alignment with the time axis, makes it possible to clearly display the switching characteristics of the local portion of the sample at a glance, and measures, for example, the storage speed of the magnetic memory. can do.
[Brief description of the drawings]
FIG. 1 is a diagram showing a basic configuration of an external magnetic field sweeping magnetic force microscope according to the present invention.
FIG. 2 is a diagram illustrating the operation of one embodiment of the present invention.
FIG. 3 is a diagram illustrating the operation of another embodiment of the present invention.
FIG. 4 is a diagram showing a basic configuration of a conventional magnetic force microscope.
FIG. 5 is a diagram showing a basic configuration of a conventional VSM.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Probe 7 Synchronous amplifier 2 Cantilever 8 Computer 3 Displacement detecting means 9 Sample stage 4 Exciting means 10 Sample 5 Moving means 11 Display 6 External magnetic field applying means

Claims (5)

A cantilever having a small probe with a coercive force greater than the maximum external magnetic field at the tip, a means for detecting displacement of the cantilever, and an excitation means for oscillating the distance of the cantilever with respect to the sample surface with a desired amplitude at a constant period. Moving means for moving the sample relative to the probe, external magnetic field applying means comprising an electromagnet capable of applying a magnetic field perpendicular or parallel to the sample, means for sweeping the magnitude of the external magnetic field, and external magnetic field An external magnetic field sweeping magnetic force microscope, comprising: a synchronous amplifier for outputting an MFM signal in synchronization with the external magnetic field, and detecting an MFM signal in synchronization with the external magnetic field while sweeping the external magnetic field to enable local magnetization measurement of the sample. . Means for driving and scanning the probe from a predetermined position to another predetermined position; means for calculating the difference between the MFM signals of the magnetic portion and the non-magnetic portion of the sample; and means for sweeping the external magnetic field from a predetermined value to an inverted predetermined value. 2. The external magnetic field sweeping magnetic force microscope according to claim 1, further comprising: a unit configured to store a value of the MFM signal difference corresponding to an external magnetic field value, and to measure a magnetization characteristic in a local portion of the sample. A means for sweeping an external magnetic field from a predetermined value to a predetermined reverse value, a means for storing a response MFM signal from a probe set at a fixed point of a standard sample in association with the external magnetic field value, and a means for storing the same external magnetic field from the detected MFM signal 2. The external magnetic field sweeping magnetic force according to claim 1, further comprising: means for performing a difference operation on the stored value corresponding to the value, and a function of compensating and removing a characteristic component unique to the device during a normal MFM operation. microscope. A means for changing the external magnetic field into a pulse having a steep rising and a steep falling; a means for storing a response MFM signal from a probe installed at a predetermined position of the sample along with an elapsed time; and a means for storing the external magnetic field and the MFM signal on a time axis. 2. The external magnetic field sweeping magnetic force microscope according to claim 1, further comprising: a unit for displaying a combination of the measured values and measuring a local switching characteristic of the sample. In a magnetic force microscope, a magnetic portion of a sample detected by driving and scanning a probe from a predetermined position to another predetermined position over a region including a magnetic portion and a non-magnetic portion while sweeping an external magnetic field from a predetermined value to an inverted predetermined value. A method of calculating a difference in MFM signal between a magnetic field and a non-magnetic portion, and making the value of the MFM signal difference correspond to the external magnetic field value to measure magnetization characteristics in a local portion of the sample.

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