JPS63318014A - Superconductive film of metal oxide - Google Patents

Abstract

PURPOSE:To provide a superconductive film of metal oxide type which raises the critical current density, by furnishing a layer of ferromagnetic metal between superconductive layers of oxide type as a pinning center fixing the line of magnetic flux. CONSTITUTION:Superconductive layers 2 and ferromagnetic metal layers 3 are laid on a base plate 1 one over another by sputtering to accomplish a film construction. In this arrangement the ferromagnetic metal layer serves as a pinning point for fixing the line of magnetic flux. This hinders intrusion of flux to lead to enhancement of the critical current density of superconductor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a metal oxide-based superconducting thin film, and particularly to a superconducting thin film having a high critical current density.

[Conventional technology]

Y-Ba-Cu=O1 and metal oxide superconductors using rare earth metals instead of Y are discussed in the Japanese Journal of Applied Physics Part 2 Letters (JJAP Part 2 Letters, special issue (1987)). These superconductors are type 2 superconductors whose electrical resistance becomes zero above the liquid nitrogen temperature and exhibit the Meissner effect.

Furthermore, even when this superconductor is made into a thin film using thin film forming techniques such as vacuum evaporation or sputtering,
It has been confirmed that it exhibits superconducting properties at temperatures above liquid nitrogen temperature.

[Problem that the invention seeks to solve]

In the above conventional technology, the critical current density is 103 to 10
'A/cd', and one major challenge is to improve the critical current density.

An object of the present invention is to provide a metal oxide-based superconducting thin film that improves critical current density.

[Means for solving problems]

In order to increase the critical current density, the objective described in item 1 is achieved by providing a layer of ferromagnetic metal between the oxide superconducting layers as a pinning center for fixing magnetic flux lines.

[Effect]

In general, pinning centers (pinning points) that are effective in increasing the critical current density of superconductors include dislocation structures introduced by processing, precipitates caused by aging, and heterogeneous points such as grain boundaries. These create a valley with low free energy for the magnetic flux lines that penetrate into the superconductor,
It is known to be a pinning point. Conventional alloy-based superconductors use precipitates, while compound-based superconductors use grain boundaries.

However, these are bulk cases, and the film thickness is several μm.
In the case of the following thin films, the provision of inhomogeneous points such as precipitates and grain boundaries has the disadvantage of affecting the crystal orientation, crystal structure, etc. of the film, and lowering the critical temperature of the original superconducting properties. In the present invention, as shown in FIG. 1, a ferromagnetic element is introduced as a pinning point. In other words, by creating a film structure in which superconducting layers and ferromagnetic metal layers are alternately laminated, the ferromagnetic metal layers act as pinning points for fixing magnetic flux lines, thereby preventing magnetic flux from entering the superconductor. Improve critical current density.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure shows the membrane structure of the invention. Superconducting layers 2 and ferromagnetic metal layers 3 are alternately laminated on a substrate by sputtering.

Table 1 shows the sputtering conditions. The sputtering targets used are YtBazCuaO7 for the superconducting layer and Fe for the ferromagnetic layer. Both are 4"
A φ-5t target was used. The substrate is Si<100>
It is.

After sputtering, the degree of vacuum is 3. Heat treatment is performed in an atmosphere in which oxygen gas is introduced at X 10-5 Torr. The heat treatment temperature is 500-600'C and the heat treatment time is 5 hours.

Table 1 and Figure 2 show the electrical resistance-temperature characteristics of only the Y-Ba-Cu-0 film. The critical temperature Tc is 86°C.

At this time, the critical current density is 5X10 at a temperature of 77K.
It was 3A/d. On the other hand, when Fe layers are alternately inserted between superconducting layers, the critical current density Jc and the Fe layer thickness d
Figure 3 shows the relationship between m.

The thickness ds of the superconducting layer is shown as a parameter.

The total thickness of the superconducting layer is approximately 1 μm. When dm=lo00 people, Jc becomes larger than when only the superconducting layer is used when dm≦100 people, and smaller than when only the superconducting layer is used when dm>100 people. Similar trends were observed for other ds.

In addition, in the area where Jc is 5 x 103A/d or more, F
The critical temperature was almost constant regardless of the thickness of the e-layer or the thickness of one superconducting layer. As described above, according to this embodiment, there is an effect that the critical current density of the oxide-based superconducting film can be significantly improved. In addition to the above examples, similar results were obtained for oxide superconductors in which a rare earth element was used instead of Y.

FIG. 4 shows a film structure when an oxide magnetic material is used for the magnetic layer. As the oxide magnetic layer, spinel type oxide (MO-
Fe203. M is a divalent metal ion such as Fe, Co, N
j, etc.) and perovskite-type oxides (M Fe Os
, M is a trivalent ion such as La, Ca, Ba, etc.). The sputtering conditions are the same as in Table 1. In this case, since the magnetic layer is an oxide, there is an effect that stability against heat treatment after sputtering film formation is improved.

[Effects of the Invention] According to the present invention, the critical current density of the oxide-based superconductor can be increased, so that when used for wiring materials, coils, etc., a large current can be passed.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the film structure of the present invention, Figure 2 is a diagram showing the relationship between resistance and temperature, and Figure 3 is a diagram showing the relationship between critical current density and Fe
A diagram showing the relationship with layer thickness, and FIG. 4 is a sectional view showing the film structure of another example of the present invention. 1...Substrate, 2...Superconducting layer, 3...Magnetic layer.

Claims (1)

[Claims] 1. Layered provskite type metal oxide superconducting material M-
It is characterized by alternating layers of Ba-Cu-O (M is Y or a rare earth metal with an atomic number of 57 to 71) and a ferromagnetic metal material (Fe, Co, Ni, Gd, etc.) or a ferromagnetic metal alloy material. Metal oxide superconducting thin film. 2. In claim 1, the thickness d of the superconducting layer
s is in the range of 25 to 1000 Å, and the thickness dm of the ferromagnetic layer is 5
A metal oxide superconducting thin film, characterized in that the layers are stacked in a range of 100 Å and ds≧dm. 3. A metal oxide superconducting thin film according to claim 1, characterized in that an oxide magnetic material is used as the material of the ferromagnetic layer.