JPS6058832B2 - Magnetic susceptibility measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for measuring the magnetic susceptibility of paramagnetic substances, diamagnetic substances, etc., and is particularly advantageous when identifying whether a substance with extremely low magnetic susceptibility is diamagnetic or paramagnetic. It is related to the equipment.

Conventionally, there have been three types of methods for measuring magnetic susceptibility as shown below in principle.

1. Measure the force exerted on a sample placed in a non-uniform magnetic field.

2.Measure the electromotive force induced in a coil placed near the sample when the sample is moved in a uniform magnetic field. 3. The external magnetic field changes due to the magnetization induced in the sample by the external magnetic field, and the change in this external magnetic field is measured.

A device based on the first principle is a magnetic balance, and a device based on the second principle is a vibrating sample magnetometer.

The present invention is based on three principles. An example of a device based on this principle is a positionless magnetometer, which is widely used in the field of rock magnetism. However, the conventional positionless magnetometer (
Other types of magnetometers (such as fluxgate magnetometers, optical pumping magnetometers, and SQ magnetometers) can measure the magnitude of minute magnetic fields and their changes, but they cannot be placed in strong magnetic fields. It is not possible to measure minute changes in strong magnetic fields. Therefore, when measuring magnetic susceptibility, it is necessary to apply an extremely weak external magnetic field and detect the even more minute changes in the magnetic field induced by it, which makes it difficult to obtain sufficiently high measurement accuracy. There were flaws. On the other hand, other magnetic field measurement devices, such as a Gaussmeter using a Hall element or an integral type magnetometer using a pickup coil, can measure strong magnetic fields, but they are less sensitive to external magnetic fields than 10-0. It does not have enough precision to measure fluctuations as small as 10-0. Therefore, they could not be used to measure magnetic susceptibility. This invention is based on nuclear magnetic resonance (NM).
By using a Gauss meter using R), minute changes in the magnetic field of several milli Gauss can be accurately measured in a magnetic field of several thousand to tens of thousands of Gauss, and magnetic susceptibility can be measured based on the principle 3 in a strong magnetic field. The purpose is to do the following.

To explain this invention based on the drawings, in FIG. 1, an NMR probe 2, a sample 3, and a movement for moving the sample parallel to the surface of the magnetic pole piece 1 are shown in FIG. A stand 4 and a fixed stand 5 are housed.

A movable base 4 made of a synthetic resin plate whose magnetic susceptibility is constant and whose magnetic field strength in the gap does not change even if it is moved 5 to 10 cm within the gap is placed on a fixed base 5. By sliding, the sample 3 placed on the moving table 4 can be brought from a position away from the probe 2 to directly below the probe. The NMR probe 2 includes a container 6 made by hollowing out a copper plate, a feedback coil 7 housed in the container, and a reference sample (for example, water added with chromium).
8, a sample coil 10 wound around the glass tube, a copper vibe 11 for holding the container 6, and a conducting wire 12 connecting the sample coil to the NMR Gaussmeter body. FIG. 2 shows the overall configuration of the NMR Gaussmeter. The NMR Gaussmeter includes the probe 2 described in FIG. 1, a signal transmitting/receiving section 14 that applies a high-frequency magnetic field to the probe and receives nuclear magnetic resonance signals generated from a sample, and a signal transmitting/receiving section 14 that receives a nuclear magnetic resonance signal generated from a sample and uses an NMR absorption signal as an error signal. It consists of an integral amplifier 15 for causing the feedback coil to perform negative feedback, and a recorder 16 for recording a voltage proportional to the negative feedback current. In the above configuration, the reference sample sealed in the glass tube of the NMR probe is brought into a nuclear magnetic resonance state by a strong DC magnetic field of several thousand to tens of thousands of Gauss formed between the magnetic pole pieces and a high frequency magnetic field from the sample coil 10. Become. The resonance condition of nuclear magnetic resonance is hν = γH (h: Planck's constant, ν: frequency of high-frequency magnetic field, γ: gyromagnetic ratio, H: DC magnetic field), and therefore γ is not known from the reference sample. H can be found by measuring ν. This is the basic principle of the NMR Gaussmeter. Now, a magnetic field is induced within the sample by the strong magnetic field formed between the magnetic pole pieces, and the induced magnetic field causes a change in the strong magnetic field near the sample.

However, since the magnetization induced within the sample is extremely small, the effect on the external strong magnetic field is also extremely small, and the external magnetic field around the sample changes only by a few milli Gauss. Therefore, the sample 3 is placed far away from the NMR probe 2, for example 3a.
Measure the magnetic field strength twice with the NMR Gaussmeter, once when the probe is placed at the position of It is possible to detect minute changes in FIG. 3 shows an example of measurement using the above-mentioned NMR Gaussmeter. The sample used was an epoxy resin formed into a disk shape with a diameter of 157 wt and a thickness of 3 layers, and manganese dioxide was added to change the magnetic susceptibility of the resin. There were three types of samples depending on the amount of manganese dioxide added (0.75%, 1.
5%, 3.0%) were prepared. From Figure 3, the magnetic field strength varies from -6 x 10-6 to +8 x 1 depending on the amount of manganese dioxide added.
It can be seen that there was a change of about 0-6 (Wb/r!l). If the amount of manganese dioxide added is plotted on the horizontal axis and the amount of change in the magnetic field is plotted on the vertical axis, the result will be as shown in FIG.

A decrease in the external magnetic field indicates that the sample is a diamagnetic material, and an increase in the air gap field indicates that the sample is a paramagnetic material. From this figure, M
It can be seen that the amount of nO2 added is about 1.8%.
In order to determine the magnetic susceptibility from the amount of change in the magnetic field, we further performed the following measurements.

That is, an oxygen-free copper wire (4) whose magnetic susceptibility is already known to be 0.85x10-6 CGSemu. 23T! Unφ) was wound to create a disk with a diameter of 15wn and a thickness of 3=, and when this was measured in a magnetic field of 2.35 Wb/a in exactly the same way as the epoxy resin, it was found that it was only 4.93 x 10-6 Wb/d. The magnetic field decreased. Therefore, the diameter of the sample in an external magnetic field of 2.35 Wb/d is 1577!77! , using a disk with a thickness of 3WL and arranging it as shown in Fig. 1, in order to convert the amount of change in the magnetic field to magnetic susceptibility, the amount of change in the magnetic field must be 0.85 x 10- 6/4.93X10-6=0.172
All you have to do is multiply by . As detailed above, according to the present invention, since the sample is placed in a strong magnetic field, the amount of change in the magnetic field is larger than in the past, and the greatly changing magnetic field is measured with extremely high accuracy (1 Kariichi ~ 1 x 1σ) using an NMR Gaussmeter. Even when the magnetic susceptibility is small, it can be measured with extremely high accuracy.

Furthermore, since the present invention has extremely few mechanically moving parts, the mechanism is simple, and complicated mechanisms such as magnetic balances, which have been widely used in the past, are not required.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing one embodiment of the present invention, and FIGS. 3 and 4 are diagrams showing measurement results using the above embodiment. 1: Magnetic pole piece, 2: NMR probe, 3: Sample, 4: Moving table, 5: Fixed table, 8: Reference sample, 14: Signal transmitting/receiving section,
16: Recorder.

Claims (1)

[Claims] 1. An NMR Gaussmeter comprising a magnet device for generating a magnetic field and an NMR probe disposed within the magnetic field;
A sample moving means for moving a measurement sample from a position far away from the NMR probe to a position close to the NMR probe, and a change in the strength of the magnetic field around the probe that occurs when the measurement sample approaches the NMR probe. A magnetic susceptibility measuring device characterized by being configured to detect.