JPH04274379A - Magnetic sensitive element - Google Patents

Abstract

PURPOSE:To prevent deterioration of a filmlike superconducting magnetic sensitive element using a magnetoresistance effect with moisture. CONSTITUTION:An oxide superconducting polycrystalline thin film is sealed in a vessel made of a material having high thermal conductivity such as aluminum nitride, silicon carbide, Ag, Ti, etc., by filling gas such as Me, He gas, etc., at a liquid nitrogen temperature or lower. Deterioration of the film due to invasion of moisture is prevented by the sealing, and it can be used stably as a magnetic sensitive element for a long period.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetically sensitive element, and more particularly to a magnetically sensitive element using an oxide superconducting polycrystalline thin film produced using a physical method.

0002

[Prior Art] Conventionally, Bi(Pb)-Sr-Ca-
Attempts have been made to utilize the magnetoresistive effect of Cu-O 2 and Y-Ba-Cu-O 2 oxide superconductors to apply oxide superconductors as magnetic sensing elements.

0003

[Problem to be solved by the invention] In the above method,
When an oxide superconductor is used as a magnetic sensing element, the oxide superconductor deteriorates due to the intrusion of H2O from the grain boundaries, and the oxide superconductor transforms from a superconducting material to a normal conducting material. It cannot be used as a magnetically sensitive element for a long period of time.

[0004] Even when a film-like material that can be miniaturized is used, in addition to chemical deterioration due to H2O, the film may be damaged by repeatedly exposing the device to temperature changes between room temperature and liquid nitrogen temperature. Since the attached H2O undergoes repeated transformations between liquid and solid, there is a problem in that the film deteriorates mechanically due to the difference in thermal expansion, resulting in a decrease in magnetic sensitivity.

[0005]

[Means for Solving the Problem] As a result of investigating the possibility of using an oxide superconducting polycrystalline thin film as a magnetic sensing element over a long period of time, the present inventors found that the contact of moisture to the superconductor The above problem was solved by blocking the .

That is, in the present invention, an oxide superconducting polycrystalline thin film produced using a physical method is placed in a closed container made of a material with high thermal conductivity, and a gas is injected into the container at a temperature below the temperature of liquid nitrogen. A magnetic sensing element is characterized in that it is filled with a gas that is in a state of.

[0007]

DETAILED DESCRIPTION OF THE INVENTION Since oxide superconductors are ceramics, they have crystal grain boundaries that are insulating phases, and for this reason, when a magnetic field is applied, the critical current density decreases rapidly. In other words, when a magnetic field is applied from the outside while a critical current is applied, resistance occurs. By utilizing this property, it becomes possible to measure magnetic fields.

[0008] As a method for producing an oxide superconducting polycrystalline thin film, there is a method that does not cause a change in composition even in minute parts of the film.
Physical methods such as sputtering, vapor deposition, laser ablation, and MBE are preferred.

When depositing the constituents of an oxide superconducting polycrystalline film on a substrate, the film deposition method may include a method of sequentially depositing each constituent on the substrate depending on the raw material for each constituent, or a combination of constituents. An example is a method of depositing using raw materials.

However, if a raw material containing all the constituent components is used, the composition of the raw material and the composition of the film deposited on the substrate will differ greatly, so it is difficult to determine the raw material composition so as to obtain the desired film composition. is difficult. In particular, in the case of a Bi-based superconducting oxide, since there are many types of constituent components, it is preferable to use the constituent components separately.

[0011] When producing a film, the superconducting film may be produced directly by heating the substrate, or by producing an amorphous film without heating the substrate and heat-treating it. In this case, the composition of the amorphous film may be any composition that becomes a superconductor after heat treatment.

[0012] The amorphous film is heat-treated for a predetermined period of time at a temperature at which each compound is formed to crystallize it. The temperature is as follows.

Bi-Pb-Sr-Ca-Cu-O system:
820-850°C Bi-Sr-Ca-Cu-O system:
850-880°C Y-Ba-Cu-O system: 90
0~1000℃ Tl-Ba-Ca-Cu-O system: 9
00~1000℃ Tl-Sr-V-O system: 800~
1000℃

700-80 before heat treatment
Preliminary calcination at 0°C for 2 to 10 hours stabilizes the properties. After heat treatment, it is cooled in a furnace.

[0015] As the substrate supporting the film, MgO, S
rTiO3, LaGaO3, LaAlO3, etc. oxide single crystal, Ag, Au, Pt, Cu with an insulating buffer layer
metals such as, semiconductors such as Si, GaAs, etc. are used.

[0016] The container housing the oxide superconducting polycrystalline thin film transfers the heat of the surrounding cooling medium to the film inside.
It is preferable to use a material with high thermal conductivity. Examples of the material include ceramics such as aluminum nitride and silicon carbide, and metals such as Ag and Ti.

The container is filled with a gas such as Ne or He that is in a gaseous state at a temperature below the liquid nitrogen temperature (77.3).

[0018] The adhesion of the oxide superconducting thin film to the container is achieved using In
Bonding is done using or Sn, etc., and the lead wire is
A connection part is provided in a sealed container and the container is pulled out from inside the container. When the container is metal, it is preferable to use metallized parts or the like.

To measure the magnetic field, the container is partially or completely immersed in a cooling solvent such as liquid nitrogen.

[0020]

[Operation] By housing the oxide superconducting polycrystalline thin film in a closed container with high thermal conductivity and filling it with gas at a temperature below the temperature of liquid nitrogen, the superconducting thin film is not affected by H2O, and , thermal fluctuations around the superconductor are also reduced due to thermal conduction of the filling gas and the container.

[0021]

[Example] Example thin films were prepared by a sputtering method. The following three types of sputtering targets were used.

■Bi0.5Pb0.5Ox (Bi2O3 and PbO
Mixed powder of) ■CaCu0.75Ox (CaCO
3 and CuO sintered powder at 950 °C)■SrCu0.7
5Ox (950℃ sintered powder of SrCO3 and CuO)

The thin film composition was adjusted by adjusting the deposition time of each target as follows.

■Bi0.5Pb0.5Ox: 6 seconds ■C
aCu0.75Ox: 58 seconds ■SrCu0.75Ox: 34 seconds

[0025] This single layer was stacked 400 times to form a 2 μm thin film.

[0026] This film (composition (Bi+Pb) 1.00S
r1.00Ca0.96Cu1.95Ox), 780
After heat treatment at 844°C for 2 hours, heat treatment was performed at 844°C for 65 hours.

The magnetic sensitivity of the superconducting film obtained by heat treatment was measured, and a magnetic sensitivity of 1875.3 μV/Gauss was obtained.

[0028] This film was placed in a container made of aluminum nitride coated with MgO 2 and sealed with In, and the inside of the container was filled with He gas.

This container was immersed in liquid nitrogen for 10 minutes and then left at room temperature for 10 minutes. This was repeated 10, 20, and 30 times, and the magnetic sensitivity was measured each time. The results were 1862.4 μV/Gauss and 18
They were 60.1 μV/Gauss and 1850.2 μV/Gauss.

Comparative Example As a comparison, a magnetically sensitive element (magnetic sensitivity: 1800.3 μV/Gauss) that was not placed in a container was immersed in liquid nitrogen for 10 minutes and then left at room temperature for 10 minutes. This repetition,
The test was repeated 10, 20, and 30 times, and the magnetic sensitivity was measured each time. As a result, the membrane deteriorated as the number of repetitions increased, 1623.1μV/Gauss and 1022.4μV/Gauss, respectively.
V/Gauss and 852.1 μV/Gauss.

[0031]

[Effects of the Invention] When the magnetically sensitive element of the present invention is used, the oxide superconducting polycrystalline thin film is blocked from H2O, so the superconducting properties do not deteriorate and the magnetically sensitive element can be used stably for a long period of time. became possible to use.

Claims (1)

[Claims] [Claim 1] An oxide superconducting polycrystalline thin film produced using a physical method is placed in a closed container made of a material with high thermal conductivity, and the film is in a gaseous state at a temperature below the temperature of liquid nitrogen inside the container. A magnetic sensing element characterized by being filled with gas.