JP2936125B2 - Magnetic bearing detection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic azimuth detecting method, and more particularly, to a magnetic azimuth detecting method using a magnetic sensor using a highly-oriented oxide superconducting polycrystalline thin film. is there.

[Conventional technology]

2. Description of the Related Art Conventionally, as a method of examining the direction of magnetism, there is a compass for examining the direction of a weak magnetic field (about 0.3 to 0.5 gauss) similar to the geomagnetism.

Recently, a magnetoresistive element using a ceramic superconductor has attracted attention. For example, Japanese Patent Application Laid-Open No. 1-138770 discloses that a superconducting material having a crystal grain boundary is superconductive at a temperature below its critical temperature. There is disclosed a magnetic field detecting device that detects an external weak magnetic field by a magnetoresistance effect in a state where a bias magnetic field slightly larger than a magnetic field that breaks a weak coupling state between crystal grains of a body is applied.

[Problems to be solved by the invention]

In the above-mentioned method, since a compass magnet can detect only a magnetic field direction of about the earth magnetism, a magnetic direction sensor having excellent magnetic sensitivity capable of measuring even 0.1 Gauss or less has been demanded.

In the method using the magnetoresistance effect of a superconductor,
Although the field strength could be measured, the orientation of the field was not always accurate given the presence of a considerable amount of bias field.

[Means for solving the problem]

The present inventors have found that when a current larger than the critical current value at a temperature below the critical temperature is applied to the oxide superconducting polycrystalline thin film, the magnetoresistance effect due to the external magnetism appears remarkably, and the bias magnetic field It was found that external criticality could be detected without the presence of Furthermore, using a highly oriented thin film as an oxide superconducting polycrystalline thin film, the magnetic sensitivity was examined by changing the angle between the magnetic field and the surface of the thin film. The inventors have found that the present invention largely depends on the angle, and have completed the present invention.

That is, the present invention relates to a highly oriented oxide superconducting polycrystalline thin film in which the magnetoresistance effect changes depending on the angle of the magnetic azimuth with respect to the thin film surface, at a temperature lower than the critical temperature and a current higher than the critical current value at that temperature. A magnetic azimuth detecting method characterized in that the magnetic field strength and azimuth are measured according to the direction of the thin film in which the magnetic field strength detected by the magnetoresistance effect is maximized by applying a magnetic field to the thin film. It is.

Since the oxide superconductor is a ceramic, it has a crystal grain boundary which is an insulating phase. Therefore, when a magnetic field is applied, the critical current density sharply decreases. That is, at a temperature lower than the critical temperature of the oxide superconductor thin film, when a current equal to or higher than the critical current at that temperature flows, a certain resistance is generated in the thin film, but this resistance further increases due to an external magnetic field.
Since the increase in the resistance value changes depending on the strength of the magnetic field, the magnetic field can be measured by using this property.

Further, the direction of the magnetic field can be determined by utilizing the orientation of the oxide superconductor. In other words, since the oxide superconductor is a plate-like crystal, when it is made into a thin film, the C axis is oriented perpendicular to the thin film surface, the magnetic sensitivity greatly depends on the anisotropy of the crystal, and the magnetic field becomes parallel to the C axis. When applied, the magnetic sensitivity is large, and when applied perpendicular to the C-axis, the magnetic sensitivity is reduced. By utilizing this property, the direction of the thin film is moved,
By determining the orientation of the thin film at which the magnetic sensitivity is maximized, the strength of the magnetic field and its orientation can be determined.

Although the reason why the magnetic sensitivity of the thin film varies depending on the direction of application of the magnetic field is not clear at present, it is considered to be largely related to the fact that the conduction surface of the superconductor is perpendicular to the C axis.

The orientation of the plate-like crystal of the oxide superconductor is evaluated using the half width of a rocking curve used for measuring the single crystallinity of the thin film as a guide. In this case, the smaller the half width of the rocking curve, the more the plate-like crystal is oriented, and it is preferable that this value is 15 ° or less.

The rocking curve is used to evaluate the crystallinity of a thin film or an epitaxial film having a certain degree of orientation.
And the diffraction intensity obtained by changing the angle (θ) of the sample. When the thin film is made of a small crystal hardness having different directions little by little, a width corresponding to the spread of the crystal orientation is generated on the diffraction peak. When this width (the half width of the rocking curve) is narrow, it means that the crystal axes are aligned, and the width is narrow and the orientation is high.

The method for producing the thin film is not particularly limited, but a physical method such as a sputtering method or a vapor deposition method is preferable because a thin film having excellent orientation can be obtained.

The composition of the manufactured thin film may be a superconductor after heat treatment according to each compound.

However, in order to obtain high magnetic sensitivity using liquid nitrogen which is inexpensive and widely used, it is desirable that the superconductor has a critical temperature of 77K or more.

Regarding the composition of the manufactured thin film, for example, Bi _a P
Within the following range in the composition formula represented by b _b Sr _1.00 Ca _c Cu _d O _x , a superconducting thin film having a critical temperature of 77 K or more can be obtained, and can be used at liquid nitrogen temperature.

If 0.5 <a <1.0 b <1.0 0.6 <c <1.2 1.4 <d <2.0 Bi is less than 0.5, it is difficult to synthesize a superconductor, and if it is more than 1.0, a Sr—Ca—Cu—O compound is formed as a grain boundary phase. Therefore, the precipitates at the crystal grain boundaries are small and the magnetic sensitivity is deteriorated. When Pb is more than 1.0, the film is easily melted, and thus a semiconductor phase is easily generated. If the Ca content is less than 0.6, a semiconductor phase is easily generated, and it is difficult to become a superconductor. 1 if more than 1.2
Although a 10K phase is generated, a large amount of an insulating phase is precipitated between the superconducting particles, which obstructs the path of the superconducting current and makes it difficult to become a superconductor. If Cu is less than 1.4, it is difficult to synthesize a superconductor, and if it is more than 2.0, the film is likely to be melted, so that a semiconductor phase is easily formed and it is difficult to become a superconductor.

In the Y-Ba-Cu-O system, YBa ₂ Cu ₃ O _x , Tl-Ba-Ca
_{Tl 2 Ba 2 Ca 2 Cu 3} O x is theoretical composition in -cu-O system.

As the substrate, MgO, SrTiO ₃ , LaGaO ₃ , oxide single crystal and polycrystal such as Al ₂ O ₃ , Ag, Au, provided with a buffer layer of an insulator,
Polycrystalline metals such as Pt and Cu and semiconductors such as Si and GaAs are used.

Substrate heating may or may not be performed during thin film production.

The raw materials used are compound powders such as oxides, carbonates and nitrates, ceramics obtained by sintering these powders, and, depending on the film forming method, individual metals, two or more metals, and metals. Organic substances and the like are used.

The prepared thin film is subjected to a heat treatment at a temperature at which each compound is generated for a predetermined time to crystallize the thin film.

For example, Bi-Pb-Sr-Ca-Cu-O system: 820-850 ° C Bi-Sr-Ca-Cu-O system: 850-880 ° C Y-Ba-Cu-O system: 900-1000 ° C Tl-Ba-Ca-Cu-O system Heat treatment is performed at 900 to 1000 ° C. Pre-calcining at 700 to 800 ° C. for 2 to 10 hours before the heat treatment is effective for stabilizing the characteristics. After the heat treatment, it is gradually cooled in the furnace.

〔Example〕

As a sputtering target, Bi _0.5 Pb _0.5 O _x (mixed powder of Bi ₂ O ₃ and PbO) CaCu _0.75 O _x (fired powder of 950 ° C. of CaCo ₃ and CuO) SrCu _0.75 O _x (sintered powder of SrCO ₃ and CuO at 950 ° C.) (Powder) was used to form a film on a MgO single crystal substrate. The deposition time for each target is as follows.

Bi _0.5 Pb _0.5 O _x ··· 9 seconds CaCu _0.75 O _x ··· 50 seconds SrCu _0.75 O _x ··· 40 seconds This deposition was used as one layer and laminated 400 times to obtain a thin film of about 2 μm. As a result of analyzing the composition of the obtained thin film by EPMA, it was (Bi + Pb) _1.10 Sr _1.00 Ca _0.70 Cu _1.32 O _x . This was heat-treated at 780 ° C. for 2 hours and then heat-treated at 835 ° C. for 65 hours.

After the heat treatment, the magnetic sensitivity of the obtained thin film was measured by a four-terminal method at a liquid nitrogen temperature (77 K) while changing the direction of an externally applied magnetic field with respect to the thin film surface.

When a magnetic field is applied from 0 to 2 gauss with a DC current (1.0 mA) larger than the critical current value (1 μA) applied to the thin film, the output generated between the voltage terminals as the resistance value of the film increases. Since the voltage changes, the value of the output voltage was evaluated in μV / Gauss. The larger the value, the higher the magnetic sensitivity. The length between the electrodes of the measurement voltage was 15 mm.

Further, the rocking curve was measured using the (0014) diffraction line of the 110K superconductor of the obtained thin film. As a result, the half width of the curve was 4.2 °, indicating that the sample was well oriented. Table 1 shows the measurement results.

The angle θ between the surface of the thin film and the externally applied magnetic field was set to θ = 0 when the magnetic direction was perpendicular to the surface of the thin film.

From the above results, the obtained thin film has magnetic sensitivity up to the order of 10 ^-5 Gauss, and by changing the direction of the thin film, if the direction of the thin film showing the maximum output voltage with respect to the magnetic field is obtained,
The direction perpendicular to the thin film at that time is the magnetic direction, and the magnetic field strength is measured with high sensitivity.

〔The invention's effect〕

According to the present invention, by using an oxide superconducting thin film having excellent C-axis orientation, a sensitivity of the order of 10 ⁻⁵ Gauss can be obtained, and the direction of the magnetic field can be easily obtained.

Continuation of front page (56) References JP-A-62-233387 (JP, A) JP-A-1-250875 (JP, A) JP-A-64-82576 (JP, A) JP-A-2-159589 (JP) JP-A-2-264879 (JP, A) JP-A 1-286978 (JP, A) JP-A-2-205784 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB Name) G01R 33/00-33/10

Claims (2)

(57) [Claims] 1. An oxide superconducting polycrystalline thin film having a high orientation in which a magnetoresistance effect changes with an angle of a magnetic azimuth with respect to a surface of a thin film, a current lower than the critical temperature and higher than a critical current value at the temperature. A magnetic azimuth detecting method, comprising: applying the applied magnetic field, changing the direction of the thin film, and measuring the strength and azimuth of the magnetic field based on the direction of the thin film in which the magnetic field strength detected by the magnetoresistance effect is maximized. 2. The method according to claim 1, wherein the oxide superconducting polycrystalline thin film is manufactured by a physical method, and the degree of orientation of the C axis of the superconducting particles is not more than 15 ° with respect to the vertical direction of the substrate as the C axis. Item (1).