JP2875295B2 - Manganese aluminum superlattice magnetic film - Google Patents

Description

The present invention relates to a structure of a magnetic film having a large saturation magnetization.

[Conventional technology]

In order to improve the performance of magnetic devices, the appearance of a magnetic material having a large saturation magnetization that cannot be obtained with a conventional magnetic material has been desired. As a magnetic material having a large saturation magnetization, an alloy mainly composed of iron has been studied, but in the case of an alloy, there is a limit value for the saturation magnetization, and the value is almost the same as the saturation magnetization of iron (2.2 terraces). It turned out to be.

Also, in recent years, superlattices in which layers made of different elements are alternately stacked have been attracting attention with the goal of exceeding the limit value of the saturation magnetization of the alloy. Such a superlattice can be formed by the technique described in JP-A-49-131679.
However, despite attempts at various locations, none have been found to exceed the saturation magnetization limit of the alloy, that is, the saturation magnetization of iron.

[Problems to be solved by the invention]

An object of the present invention is to provide a magnetic thin film having a saturation magnetization exceeding a limit value of a saturation magnetization of an alloy which cannot be obtained by the conventional technique.

Also, when forming a superlattice thin film, the present inventors paid attention to the film thickness and the atomic arrangement on the surface of the substrate, and aimed to form a thin film having a predetermined crystal orientation and to reliably show its magnetic properties.

[Means for solving the problem]

The above object can be achieved by a manganese-aluminum superlattice magnetic film in which a manganese layer having a thickness of 2 to 10 atomic layers and an aluminum layer are alternately stacked.

The thickness of the aluminum layer is desirably 1 to 10 atomic layers.

The crystal structure of the manganese-aluminum superlattice can be a tetragonal system, and its four-fold rotation axis can be parallel to the lamination direction of the superlattice magnetic film. As the substrate surface at this time, a (001) plane of a single crystal having a face-centered cubic lattice or a plane equivalent thereto can be used. Alternatively, a (001) plane of a single crystal having a body-centered cubic lattice or a plane equivalent thereto can be used.

[Action]

The saturation magnetization of the magnetic material, regardless of alloy or multilayer film,
Determined by the electronic structure. This electronic structure can be simply represented by a density of states curve, that is, a curve showing the relationship between the energy of electrons and the density of states, that is, the maximum allowable number of electrons capable of having that energy.

This state density curve is a curve schematically shown in FIG. Energy, indicated as E _F in the figure is determined by the composition and structure of a Fermi energy material. In general, any electronic energy even lower than about E _F in the material, electrons are not present high energy than about E _F. Features of the ferromagnetic material is that the state density is high in this E _F, in a state density curve having a peak at E _F. And, in general, a large saturation magnetization the greater the density of states at E _F.

In consideration of the above points, in the study of the present invention, attention was paid to the superlattice, and a state density curve was obtained by theoretical calculation for a combination of various elements. According to this theoretical prediction, a superlattice film in which manganese layers and aluminum layers were alternately laminated was prepared, and the saturation magnetization was measured. As a result, it was found that the film had a large value.

The above-mentioned density-of-states curve for a superlattice magnetic film composed of a manganese layer and a manganese-aluminum layer is obtained as shown in FIG. Unlike iron and alloys, density of states at the Fermi energy E _F vicinity extremely large compared to the density of states at the other energy. That is, the condition for having a large saturation magnetization is satisfied.

This state density curve does not take into account the direction of electron spin. FIG. 9 shows a state density curve obtained in consideration of this. In a ferromagnetic material, in a magnetized state, there are generally + spin and -spin whose directions are different from each other by 180 degrees.
This figure shows the state density curves of both spins separately. The saturation magnetization is proportional to the difference between the numbers of electrons of both spins existing in the energy region equal to or lower than the Fermi energy.
That is, it is proportional to the difference between the areas of the hatched portions of both spins in the figure. Therefore, as is clear from this density of state curve, in the manganese-aluminum superlattice magnetic film,
Most of the electrons below the Fermi energy have a + spin, and the difference between the numbers of electrons of both spins is very large. For this reason, this superlattice magnetic film has a large saturation magnetization.

〔Example〕

Embodiment 1 Hereinafter, Embodiment 1 of the present invention will be described with reference to FIG. In this method, an aluminum single crystal having a face-centered cubic lattice is used as a substrate, and 500 layers of a manganese layer and an aluminum layer are alternately epitaxially grown by vacuum evaporation on the (001) plane. The degree of vacuum was 10 ⁻¹⁰ Torr, the deposition rate was 2 ° / s, and the substrate temperature was 260 ° C. When such lamination was performed, the lamination portion became tetragonal, and the four-fold rotation axis (c-axis) coincided with the lamination direction. The thickness of the film was fixed to the thickness of the monoatomic layer for the aluminum layer, and the thickness of the manganese layer was varied.

FIG. 2 shows the result of measuring the saturation magnetization of such a sample. The vertical axis represents the saturation magnetization, and the horizontal axis represents the thickness (the number of atomic layers) of the manganese layer. As is apparent from the figure, the limit value of the saturation magnetization of the alloy (about 2.2
It has a saturation magnetization exceeding Tesla).

Embodiment 2 Embodiment 2 of the present invention will be described with reference to FIG. this is,
A manganese layer and an aluminum layer are laminated on the (001) plane of aluminum single crystal by epitaxial growth in 500 layers each. The growth conditions are the same as in the first embodiment.
As for the film thickness, the thickness of the aluminum layer was fixed to four atomic layers, and the thickness of the manganese layer was changed. FIG. 4 shows the relationship between the saturation magnetization and the manganese layer thickness in this case. The tendency is the same as the case where the thickness of the aluminum layer is the thickness of the monoatomic layer. However, in this case, the thickness exceeding the limit value of the saturation magnetization of the alloy is between 4 and 10 atomic layers of the manganese layer.

Third Embodiment A third embodiment of the present invention will be described with reference to FIG. this is,
A manganese layer and an aluminum layer are alternately stacked on the (001) plane of a molybdenum single crystal having a body-centered cubic lattice by epitaxial growth by 500 layers. The growth conditions are the same as in the first embodiment. The thickness of the manganese layer was variously changed while the thickness of the aluminum layer was fixed to a monoatomic layer. As a result of measuring the saturation magnetization of such a sample, characteristics similar to those shown in FIG. 2 were observed. In this example, manganese was first deposited on a (001) oriented molybdenum single crystal, but the same result was obtained when the stacking order was changed and aluminum was deposited first.

Embodiment 4 Embodiment 4 of the present invention will be described with reference to FIG. this is,
As in Example 3, 500 layers of manganese and aluminum were epitaxially laminated on the (001) plane of molybdenum single crystal. The thickness of the aluminum layer was fixed at a thickness of 4 atomic layers, and the thickness of the manganese layer was changed. As a result of measuring the saturation magnetization of such a sample, characteristics similar to those in FIG. 4 were observed. Further, by changing the lamination order from the present embodiment,
Similar results were obtained when an aluminum layer was first deposited on a (001) oriented molybdenum substrate.

Furthermore, the saturation magnetization of a sample in which a manganese layer and an aluminum layer were alternately stacked on various substrates with different layer thicknesses was examined, and it was found that the value exceeding the limit value of the saturation magnetization of the alloy was found. The thickness of the layer was 2 to 10 atomic layers.

When the thickness of the manganese layer was not 2 to 10 atomic layers, only the saturation magnetization was reduced, and it was still a ferromagnetic material. When the thickness of the aluminum layer was changed, the value of the saturation magnetization changed depending on the thickness of the manganese layer. In general, when the thickness was 10 atomic layers or less, a large saturation magnetization was obtained. When the thickness of the aluminum layer was larger, the saturation magnetization decreased with the thickness, but the ferromagnetism was maintained.

Comparative Example In the case where a manganese-aluminum superlattice was formed on the (111) plane of aluminum single crystal and the (111) plane of molybdenum single crystal, even when the layers were laminated with the same layer thickness as in the example, the saturation magnetization was the same as in the example. Was 1/10 or less.

Further, the saturation magnetization in the case of using polycrystalline and amorphous glass of aluminum and molybdenum for the substrate was about 1/5 of that of the example compared with the same layer thickness.

〔The invention's effect〕

According to the present invention, it is possible to provide a ferromagnetic material having a saturation magnetization exceeding the limit value of the saturation magnetization of the alloy, so that it is possible to improve the performance of various magnetic devices.

[Brief description of the drawings]

FIG. 1 is a sectional view of Embodiment 1 of the present invention as viewed from the [100] direction, FIG. 2 is a characteristic diagram of Embodiment 1 of the present invention, and FIG. 3 is a view of Embodiment 2 of the present invention as viewed from the [100] direction. FIG. 4 is a cross-sectional view, and FIG.
5 and 6 are cross-sectional views of Example 3 and Example 4 of the present invention, respectively, as viewed from the [100] direction. FIG. 7 is a diagram showing a state density curve of a general electron. FIG. 8 is a diagram showing a state density curve of electrons in a manganese-aluminum superlattice, and FIG. 9 is a diagram showing a state density curve of electrons in a manganese-aluminum superlattice in consideration of spin polarization. 1 ... Aluminum atom, 2 ... Manganese atom, 3 ...
Molybdenum atom.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01F 10/12

Claims (7)

(57) [Claims] 1. A manganese-aluminum superlattice magnetic film, wherein manganese layers and aluminum layers each having a thickness of 2 to 10 atomic layers are alternately laminated. 2. The manganese-aluminum superlattice magnetic film according to claim 1, wherein said aluminum layer has a thickness of 1 to 10 atomic layers. 3. The manganese-aluminum superlattice magnetic film according to claim 1, wherein the crystal structure is tetragonal.
A manganese-aluminum superlattice magnetic film whose rotation axis is parallel to the lamination direction. 4. A manganese-aluminum superlattice magnetic film according to claim 3, wherein a (001) plane of a single crystal having a face-centered cubic lattice or a plane equivalent thereto is used as the substrate. 5. A manganese-aluminum superlattice magnetic film according to claim 4, wherein said substrate is an aluminum single crystal. 6. A manganese-aluminum superlattice magnetic film according to claim 3, wherein a (001) plane of a single crystal having a body-centered cubic lattice or a plane equivalent thereto is used as the substrate. 7. A manganese-aluminum superlattice magnetic film according to claim 6, wherein said substrate is a single crystal of molybdenum.