JPS63221270A - Vibration sample type magnetometer - Google Patents

Abstract

PURPOSE:To measure fine magnetic moment with high accuracy and high efficiency by constituting the magnetic pole piece of a vibration sample type magnetometer as discontinuous magnetic pole pieces, i.e. a structure body wherein an eddy current and wide-range magnetic wall movement are suppressed. CONSTITUTION:The vibration sample type magnetometer has a detection coil arranged nearby the magnetic pole piece 1 of an electromagnet constituted by winding an exciting coil 3 around a yoke 2 having a couple of mutually opposite magnetic pole surfaces 2a and fitting thin plate lamination type magnetic pole pieces 1 to the magnetic pole surfaces 2a. A DC current is supplied to the exciting coil 3 to produce a magnetic field in the gap 1a between both magnetic pole pieces 1 and a sample which is magnetized by this magnetic field is vibrated to detect induced electromotive force generated at the detection coil, thereby measuring the magnetic moment of the sample. At this time, the magnetic pole pieces 1 are constituted as discontinuous magnetic pole bodies so as to suppress eddy currents and wide-range magnetic wall movement.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a vibrating sample magnetometer, and in particular, to a vibrating sample type magnetometer, particularly for measuring minute magnetic moments of minute samples, magnetic thin film materials, etc. with high precision and high efficiency. [Background Art] In recent years, magnetic thin film materials have been actively researched in fields such as magnetic disks. Regarding magnetic thin film materials,
A small magnetic moment, e.g. 3XLO-3emu
(3.8×10.-”wb-m) or less magnetic moment must be measured with high precision. Also, in order to speed up development, the measurement time must be short and the measurement must be performed with high efficiency.

A vibrating sample magnetometer is most suitable for measuring such minute magnetic moments, and many of this type are commercially available. The measurement principle is, for example, as described in "Physics of Ferromagnetic Materials (Part 1), p. 49, published by Shokabo, 1983", a detection coil is placed near the magnetic pole piece of the electromagnet, and the detection coil is placed in the magnetic pole gap.
The sample is vibrated at about 80°C, and the induced electromotive force generated in the detection coil is amplified and measured. At this time, a surface magnetic pole corresponding to the mirror image of the magnetized sample is generated on the magnetic pole surface of the electromagnet, and lines of magnetic force from the sample are sucked into the magnetic pole surface. So that you can take advantage of this,
The detection coil surface is placed parallel to the magnetic pole surface to increase signal strength.

[Problems to be Solved by the Invention] The above-mentioned prior art generally uses a block of electromagnetic soft iron, that is, a bulk electromagnetic soft iron, as the magnetic pole piece of the electromagnet. Therefore, no consideration is given to Barkhausen noise caused by domain wall movement when changing the generated magnetic field, and this Barkhausen noise is detected by the detection coil, resulting in an increase in noise. was there. This is especially true at 10 where the pole piece approaches magnetic saturation.
When the generated magnetic field is reduced from ke (8X 10'A/m) or higher, below 4kOe (3xlO'A/m),
It was remarkable. Furthermore, in order to suppress Barkhausen noise, since this noise is pulse-like and has a wide frequency range, it was necessary to set the time constant to about 1 second. Therefore, highly accurate measurement requires a measurement time of 20 to 30 minutes per sample, resulting in poor measurement efficiency.

Furthermore, since the magnetic pole piece is a block of electromagnetic soft iron, when the frequency increases to 807, the surface magnetic pole due to the mirror image does not sufficiently appear due to eddy current loss.

For this reason, there was also a problem that the signal strength did not rise to the theoretical value, and the signal/noise ratio (S/N ratio) with respect to the above-mentioned noise could not be increased.

Commercially available vibrating sample magnetometers using the above magnetic pole pieces are:
Due to Barkhausen noise, 5X10-s-I
XIO-'emu (6,3X10-"-1,3X10
An error of about -1 to bm) will occur during measurement.

The size was not negligible, and the signal strength was also low due to the influence of eddy currents.

In this way, conventional vibrating sample magnetometers that used bulk electromagnetic soft iron as magnetic pole pieces had a reduced detection ability at a frequency of 80 Hz and generated Barkhausen noise when sweeping the magnetic field. When measuring the moment, there were problems such as ◎ poor measurement accuracy and ◎ long measurement time and poor measurement efficiency.

An object of the present invention is to provide a vibrating sample magnetometer capable of measuring minute magnetic moments with high precision and high efficiency by improving the problems of the prior art described above. .

[Means for Solving the Problems] The structure of the vibrating sample magnetometer according to the present invention for improving the above problems is such that an excitation coil is wound around a yoke having a pair of opposing magnetic pole surfaces, and A detection coil is disposed near the magnetic pole pieces of an electromagnet having magnetic pole pieces attached to each of its faces, and a magnetic field is generated in the gap between the two magnetic pole pieces by flowing a direct current to the excitation coil, and this magnetic field causes magnetization. In the vibrating sample magnetometer, the magnetic moment of the sample can be measured by vibrating the sample and detecting the induced electromotive force generated in the detection coil. It is made into a magnetic pole piece.

More specifically, the magnetic pole pieces have a structure that suppresses eddy currents and wide range domain wall movement.

[Operation] First, the removal of Barkhausen noise will be explained. Barkhausen noise generated from the yoke of the electromagnet is significantly reduced by making the magnetic pole pieces discontinuous, which suppresses domain wall movement.

Therefore, measurement efficiency is improved and measurement accuracy is also improved.

Next, the increase in signal strength will be explained. Since the frequency characteristics of the magnetic pole piece are good, the mirror image magnetic moment with respect to the sample vibration frequency of about 80 Hz is large. therefore,
As more lines of magnetic force are drawn into the magnetic pole piece,
Signal strength increases.

[Embodiments] Before entering into the explanation of the embodiments, basic matters related to the present invention will be explained.

The vibrating sample magnetometer of the present invention has a discontinuous magnetic pole piece that can suppress eddy currents and domain wall movement. An embodiment of this configuration is a laminated thin plate type in which thin plates with a thickness of 1 mm or less are laminated in a direction perpendicular to the magnetic pole surface.A bundle type in which two strips of magnetic pole pieces with a thickness of 1 m or less are bundled in a direction perpendicular to the magnetic pole surface. The magnetic pole piece 9 is a powder-molded magnetic pole piece that is compression-molded from powder having a grain size of about 100 μm or less.

By configuring it in this way, ■ eddy currents can be suppressed, increasing the signal strength, and ■ magnetic transfer can be suppressed, eliminating Barkhausen noise and improving measurement efficiency. Moreover, measurement errors can be reduced.

Note that the material for these magnetic pole pieces is a highly saturated magnetic material having a saturation magnetic flux density of 1.5 T or more, such as an Fe-Co alloy, in consideration of its suitability for electromagnets.

Fe-8i alloy gFeAQ alloy etc. are preferable.

The present invention has been made based on the above-mentioned basic matters, and will be explained below with reference to Examples.

A first example will be described.

FIG. 1 is a perspective view showing details of the vicinity of the thin plate laminated magnetic pole piece of a vibrating sample magnetometer according to a first embodiment of the present invention, and FIG. 2 is a schematic diagram showing the configuration of this vibrating sample magnetometer. 3 are front views showing the main parts of this vibrating sample type magnetometer.

In the figure, reference numeral 10 indicates an exciting coil 3 wound around a yoke 2 having a pair of opposing magnetic pole surfaces 2a;
5 is a detection coil disposed near the thin plate laminated magnetic pole piece 1; connected.

An amplifier capable of amplifying the induced electromotive force generated in the detection coil 5 due to a change in magnetic flux and measuring this as a magnetic moment; 4 is a sample whose magnetic moment is to be measured;
Reference numeral 6 denotes a vibrator that can vibrate the sample 4 in the vibration direction 8 at about 807 degrees.

The thin plate laminated magnetic pole piece 1 has a thickness of 0.5 ann and is made of Fa-Co (50
wt%) alloy thin plates 1a are stacked in a direction perpendicular to the magnetic pole face 2a to form a columnar shape. Magnetic pole face 2a
The reason why the layers are stacked in a direction perpendicular to the magnetic pole surface 2a is that eddy currents are generated parallel to the magnetic pole face 2a.

In addition, 9 is the line of magnetic force, 11 is the magnetic moment of sample 4,
12 is the mirror image magnetic moment.

With this configuration, when the sample 4 is vibrated in the vibration direction 8 by the vibrator 6, the domain wall movement is at most the same as that of the thin plate 1a.
It is suppressed to about the thickness of . Therefore, the induced electromotive force generated in the detection coil 5 due to Barkhausen noise generated from the yoke 2 is significantly reduced.

Furthermore, since the thin plate laminated magnetic pole piece 1 is itself a discontinuous body, generation of eddy currents is prevented, and the frequency characteristics of the magnetic pole piece 1 are improved. Therefore, the mirror image magnetic moment 12 with respect to the sample vibration frequency of about 80 degrees becomes large, and the number of magnetic lines of force 9 absorbed by each thin plate laminated pole piece increases, and the signal intensity increases.

Next, regarding this thin plate laminated type magnetic pole piece 1, the magnetic pole piece thickness h
The changes in the signal/noise ratio (S/N ratio) when (see Figure 1) are varied, and the changes in the S/N ratio when the specific number is varied are shown using diagrams. I will explain in detail.

FIG. 4 shows the magnetic pole piece thickness-S/N of the thin plate laminated type magnetic pole piece.
The fifth graph in the ratio characteristic diagram is the time constant -S of this thin plate laminated magnetic pole piece.
/N ratio characteristic diagram.

FIG. 4 shows a case where the distance Nd between the sample 4 and one side of the magnetic pole (see FIG. 3) is 15+m, and the sample vibration frequency is 807. As is clear from this figure, the magnetic pole piece thickness h is 3Tm
It can be seen that the S/N ratio is improved by about 15 dB when the value is above.

In addition, FIG. 5 shows a thin plate m-type magnetic pole piece 1 (pole piece thickness h=
5nwn) and the magnetic pole piece of a conventional electromagnetic soft iron block (however, the magnetic pole piece thickness is 5 mm). From this figure, the time constant at which the S/N ratio starts to decrease is 400 m5 for the magnetic soft iron block magnetic pole piece, whereas it has been improved to 40 m5 for the thin plate laminated type magnetic pole piece 1.

In this embodiment, the thin plate 1a has a thickness of 0.5n*, but the same effect can be obtained if the thin plate has a thickness of 1 mm or less.

Further, in this embodiment, the thin plate laminated magnetic pole piece 1 is cylindrical in shape, but the same effect can be achieved even if the thin plate laminated magnetic pole piece 1 is in the shape of a truncated cone.

Next, the embodiment shown in FIG. 2 will be described.

FIG. 6 is a perspective view showing details of the vicinity of the bundle type magnetic pole piece of the vibrating sample magnetometer according to the second embodiment of the present invention.

In FIG. 6, the same parts as in FIG. 1 are denoted by the same numbers. The IA is a bundle type magnetic pole piece which is formed into a columnar shape by bundling strips 1b made of Fe-Go (50wt%) alloy in a direction perpendicular to the pole face 2a and having a thickness of 0.5 mm. It is.

A vibrating sample magnetometer equipped with this strip type magnetic pole piece IA also
Similar to the embodiment shown in FIG. 1, the magnetic pole pieces IA can suppress domain wall movement and prevent the generation of eddy currents, allowing minute magnetic moments to be measured with high precision and high efficiency. be able to.

Note that the same effect can be achieved if the thickness is 1 m or less.

Next, the embodiment shown in FIG. 3 will be described.

FIG. 7 is a perspective view showing details of the vicinity of a powder molding type magnetic pole piece of a vibrating sample type magnetometer according to a third embodiment of the present invention.

In FIG. 7, the same parts as in FIG. 1 are denoted by the same numbers. And, the diameter of one particle of IB is about 5Qμmφ
The material is Fe-Co (50wt%) alloy powder 1c.
This is a powder molded magnetic pole piece that is compression molded into a cylindrical shape.

The vibrating sample magnetometer equipped with this powder-molded magnetic pole piece IB also suppresses domain wall movement and prevents the generation of eddy currents by the magnetic pole piece IB, as in the embodiment shown in FIG. It is possible to measure minute magnetic moments with high precision and high efficiency.

Note that the same effect can be achieved if the particle size of the powder is about 100 μm or less.

In each of the above embodiments, the material of the magnetic pole pieces is all F.
e -G o (50 wt%) alloy, but the material of the magnetic pole piece is not limited to this, and may be any material that is effective in a magnetic field of 10 kOe (8 x 10 SA/m) or higher, which is normally used for electromagnets. It is desirable that the saturation magnetization (saturation magnetic flux density) is 15KG (1.5T) or more.Those that satisfy this are Fe-Go gold alloy Fe-5i (15wt% or less) alloy, FeAΩ
(15 wt% or less) There are highly saturated magnetic materials such as alloys.

Using these materials, we manufactured a thin plate laminated magnetic pole piece l2-bundle type magnetic pole piece IA and a powder molded magnetic pole piece IB, and investigated their S/N increase, minimum thickness, and minimum time constant. , shown in the following table.

In this table, the S/N increase indicates the difference between the S/N ratio at the pole piece thickness h=o and the saturation value of the S/N ratio, with reference to FIG. Referring to Figure 4, S
Denotes the pole piece thickness h at which the IN ratio decreases by 3 dB from its saturation value, and the minimum time constant designates, with reference to FIG. 5, the time constant at which the S/N ratio decreases by 3 dB from its saturation value.

As is clear from this table, similar effects can be obtained no matter which of the above materials is selected.

In addition to the above-mentioned materials, for example, a sintered body of ferrite thread can also be considered. However, the saturation magnetization is 4kG (0,4
T) or less, the magnetic field generated by the electromagnet is 4kOe (3
, 2 x 10 sA/m) or less, the magnetic pole piece becomes magnetically saturated. Therefore, sintered bodies of ferrite threads are only effective below 3 kOe (2,4X 10'A/m) where magnetic saturation does not occur.

[Effects of the Invention] As described in detail above, according to the present invention, eddy currents can be suppressed, so signal strength can be increased and a high S/N ratio can be obtained.

Further, since Barkhausen noise can be significantly reduced, measurement can be performed with a short time constant, measurement time can be shortened, and measurement accuracy can also be improved.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the details of the vicinity of the thin plate laminated magnetic pole piece of a vibrating sample magnetometer according to the first embodiment of the present invention, and FIG. 2 is a schematic diagram showing the configuration of this vibrating sample magnetometer. 3 is a front view showing the main parts of this vibrating sample type magnetometer, FIG. 4 is a magnetic pole piece thickness -3/N ratio characteristic diagram of the thin plate laminated type magnetic pole piece, and FIG. 5 is a graph showing the pole piece thickness -3/N ratio characteristic. Time constant-S/N ratio characteristic diagram of this thin plate laminated magnetic pole piece, No. 6
The figure is a perspective view showing details of the vicinity of the magnetic pole pieces of the bundle type of the vibrating sample magnetometer according to the second embodiment of the present invention, and FIG. 7 is the vibrating sample type magnetometer according to the third embodiment of the present invention. FIG. 2 is a perspective view showing details of the vicinity of a powder-molded magnetic pole piece of the magnetometer. 1... Thin plate laminated type magnetic pole piece, IA... Strip type magnetic pole piece. IB...Powder molding type magnetic pole piece, 1a...Thin plate, lb.
...Strip body, 1c...Powder, 2...Yoke, 2a...
・Magnetic pole surface, 3... Excitation coil, 4... Sample, 5...
・Detection coil, 6... Exciter, 7... Amplifier, 10
...Electromagnet, 11...Magnetic moment.

Claims (1)

[Scope of Claims] 1. An excitation coil is wound around a yoke having a pair of opposing magnetic pole faces, and a detection coil is disposed near the magnetic pole piece of an electromagnet having a magnetic pole piece attached to each of the magnetic pole faces. ,
By passing a direct current through the excitation coil, a magnetic field is generated in the gap between the two magnetic pole pieces, the magnetized sample is vibrated by this magnetic field, and the induced electromotive force generated in the detection coil is detected. A vibrating sample magnetometer capable of measuring a magnetic moment, characterized in that the magnetic pole piece is a discontinuous magnetic pole piece. 2. The vibrating sample magnetometer according to claim 1, wherein the discontinuous magnetic pole piece is a thin plate laminated type magnetic pole piece in which thin plates with a thickness of 1 mm or less are laminated in a direction perpendicular to the magnetic pole surface. . 3. The vibrating sample magnetometer according to claim 2, wherein the thin plate is made of a highly saturated magnetic material. 4. The vibrating sample type magnetic force according to claim 1, wherein the discontinuous magnetic pole piece is a bundle-type magnetic pole piece in which strips having a thickness of 1 mm or less are bundled in a direction perpendicular to the magnetic pole surface. Total. 5. The vibrating sample magnetometer according to claim 4, wherein the strip is made of a highly saturated magnetic material. 6. The vibrating sample type magnetometer according to claim 1, wherein the discontinuous magnetic pole piece is a powder-molded magnetic pole piece obtained by compacting powder with a particle size of about 100 μm or less. 7. The vibrating sample magnetometer according to claim 6, wherein the powder material is a highly saturated magnetic material.