JPS6055601A - Soft magnetic thin film - Google Patents

Abstract

PURPOSE:To obtain a superior soft magnetic thin film in a wide area of use conditions by piling up respective one layer or more of a crystalline soft magnetic thin film and an amorphous soft magnetic thin film. CONSTITUTION:A crystalline soft magnetic thin film and an amorphous soft magnetic thin film are piled up. The magnetic wall having a thick amorphous has large mobility, but difficulty of forming a magnetic zone. The magnetic wall having a relatively thin crystalline material has small mobility, but easiness of forming a reverse magnetic zone. A parameter of a read-out characteristic, that is, an initial magnetic permeability and a parameter of a write characteristic, that is, a maximum magnetic permeability are denoted by mui and mumax respectively. Then, as to mui dependent on magnitude of mobility of a magnetic wall, an amorphous is superior and a crystalline material is inferior. On the contrary, as to mumax dependent on easiness of forming a reverse magnetic zone, a crystalline material is superior and an amorphous is inferior. Large mui and mumax characteristics which can not be realized in each single film can be obtained by piling up an amorphous soft magnetic film and a crystalline soft magnetic film.

Description

[Detailed description of the invention] The present invention relates to a soft magnetic thin film.

With the recent increase in the density of magnetic recording, the importance of soft magnetic thin films is increasing day by day. However, in addition to the general problems associated with soft magnetic materials, soft magnetic thin films have many problems due to their thin film shape.

These problems fundamentally come down to the problems of domain wall mobility and domain wall generation, which are most important in the magnetization process of soft magnetic materials. Specifically, we will discuss the common problems with soft magnetic materials: 1) large magnetic anisotropy, 2) large magnetostriction, 3) crystalline and magnetic defects in the structure, and 4) defects caused by the thin film. 5) Surface and interface irregularities 6) Magnetic domain structure is different from that of the bulk.

etc. In the case of a thin film, these materials inhibit domain wall movement more effectively, making it more difficult to improve the soft magnetic properties of a soft magnetic film than with bulk materials.

When discussing the soft magnetic properties of materials, the measurement conditions are extremely important. This is because the magnetic properties of materials are often highly nonlinear; for example, in certain situations, A
is better than B, but the opposite could easily happen in other situations. Therefore, the magnetic properties of a substance have no meaning unless they are evaluated under the same conditions as the environment in which it is used. This also shows that when one material is used in multiple situations, it is difficult to develop a material that is good in all situations.

The most important factors regarding the above-mentioned change in magnetic properties due to measurement conditions are frequency and magnetic flux density. As an example 3%81-
The cases of F e and 50% N i -F e are shown in FIGS. 1 and 2. Figure 1 shows the frequency dependence of loss, and the second
The figure shows the dependence on magnetic flux density. As is clear from the figure, at a certain point, the magnitude of the loss, that is, the quality of the soft magnetic properties, is reversed.

Now, since soft magnetic materials used in transformers and the like are generally used at a constant frequency and a constant magnetic flux density, the usage conditions are relatively simple. However, the soft magnetic materials used for magnetic recording, for example in magnetic heads, are used with a very large magnetic flux density when writing, and conversely with a very small magnetic flux density when reading. , the usage situation will have two extreme aspects. Therefore, it is extremely difficult to develop a material that is excellent in both properties.

The materials currently being researched as soft magnetic thin film materials for magnetic recording can be roughly divided into crystalline materials and amorphous materials. In the process of developing and researching these two materials, we discovered that they have complementary magnetic properties.

By laminating these two materials, the present invention realizes a soft magnetic thin film that is excellent as a whole under a wide range of usage conditions.The facts we have discovered are illustrated in FIGS. 3 and 4. FIG. 3 shows the frequency dependence of the initial magnetic permeability (Ji), which is considered to be a parameter of the readout characteristics. Further, FIG. 4 shows the frequency dependence of the maximum magnetic permeability μm1LX, which is considered to be a parameter of the writing characteristics. In both cases, the vertical axis is a relative scale. All samples were formed on Pyrex glass by sputtering and had a thickness of 1 μm. In this example, Oo-Zr-Nb is shown as a representative example of amorphous properties, and sendust is shown as an example of a crystalline property, but other substances exhibit similar trends. As is clear from the figure, at the frequency (~MHgl) used in high-density magnetic recording, amorphous is overwhelmingly superior in μm, but crystalline is superior in μmaX. Since this characteristic is a phenomenon universally found in the amorphous and crystalline materials that we investigated, it is thought that this is a phenomenon related to the fundamentals of amorphous and crystalline films. A discussion on this will be presented below, and it is certain that both μm and μxnax are large and the material is an ideal soft magnetic material. However, in our experiments, the frequency range from several 100 KHz to several MHss
In the IjL number band, the only results obtained were that when the value of μm is large, μmaX is small, and conversely, when μWaX is large, μm is small. This suggests that there is a basic principle that μm and μmax are difficult to coexist, and that amorphous and crystalline materials exhibit opposite effects. Therefore, let us consider what is the factor that determines the size of μm and μmax. Simply put, the factors can be said to be the ease of movement of domain walls for μm, and the ease of forming reverse magnetic domains for μm1LX. Furthermore, it can be said that what lies at the root of this is the thickness of the domain wall. ff1l&
The thickness δ of i is simply expressed as follows.

δocPi Here, mu is an exchange constant and K is an anisotropy constant.

Furthermore, if the mobility of the domain wall is σ, then σ is defined as V=σH, where υ is the moving speed and H is the external magnetic field. Further, σ is expressed using A and K mentioned above. Therefore, as is clear from the above two equations, σ ■ δ In other words, the mobility of the domain wall is proportional to the thickness of the WB wall.

Regarding reverse magnetic domains, it can be said that the thicker the domain wall, the more difficult it is to form reverse magnetic domains.

Generally, when a reverse magnetic domain is formed, something that will support its formation, such as a spike magnetic domain formed around a defect or impurity in a magnetic material, is required. However, if there is a distribution in the size of these defects or impurities, if the size is smaller than a certain value proportional to the thickness of the domain wall, a spike domain cannot be generated around it, and this becomes a barrier for the formation of reverse magnetic domains. I can't do anything.

Therefore, as the thickness of the domain wall increases, the number of grasses that are effective in forming reverse magnetic domains decreases. Therefore, as the thickness δ of the domain wall increases, it becomes difficult to form reverse magnetic domains.

Now, from the above two things, it is amorphous. crystalline μm
Let us consider how the 1 μmax characteristic is explained. First, it can be said that the major difference between amorphous and crystalline materials is the difference in anisotropy caused by their structures. Soft magnetic materials inherently have a small K, but thin films are susceptible to microscopic and macroscopic variations in their composition due to their manufacturing methods. Regarding macroscopic fluctuations, it is actually observed that the composition of various multi-component alloy films varies by several percent. Regarding microscopic fluctuations, most of the films formed show a columnar structure, and the interface and inner &1SII? : Also, a compositional variation of about several percent is observed. Therefore, consideration must be given to the fact that such compositional fluctuations originally exist in a thin film state. Therefore, even if it appears macroscopically isotropic, a thin film of a crystalline soft magnetic material is considered to have a large K due to compositional fluctuations microscopically.

However, in an amorphous soft magnetic material in which anisotropy is difficult to occur due to its structure, it is considered that it still has a small K even when the above-mentioned compositional variation is taken into account. The locally large K of this crystalline material and the small K of the amorphous material create a difference in domain wall thickness, which is the characteristic μmIμm&
It is thought that the characteristics of X are determined. As shown above, the thickness δ of the domain wall is proportional to J' by 7KVC. Here, the exchange constant M is roughly proportional to the Curie temperature, and there is no big difference between crystal and amorphous. Therefore, due to the difference in K between crystalline and amorphous materials, crystalline soft magnetic materials have thinner domain walls than amorphous soft magnetic materials, whereas amorphous materials have thicker domain walls. In other words, as discussed earlier, a thick amorphous domain wall has a high mobility, but it is difficult to form a reverse magnetic domain. Furthermore, although the relatively thin domain walls of crystalline materials have low mobility, reverse magnetic domains are likely to be formed. Therefore, μm, which depends on the degree of mobility of the domain wall, is good for amorphous and bad for crystalline. Conversely, μmax, which depends on the ease of forming reverse magnetic domains, is good for crystalline materials and bad for amorphous materials.

The above consideration shows that the difference in structure between crystalline and amorphous causes a difference in the thickness of the domain wall, which determines the characteristic μm and μmax values of these two types of materials.

I thought it was. Although it is difficult to directly measure the thickness of a domain wall, FIG. 5 is shown as data supporting the above consideration. The vertical axis shows the number of domain walls, and the horizontal axis shows the magnetic flux density. The sample ■ and ■ are amorphous and ■ Oo-11' e
-81-]j, ■F e -N i -81-B. ■ is crystalline and has 3% 81-Fe. As is clear from the figure, in all amorphous materials, the number of domain walls does not increase even when the magnetic flux density is increased, indicating that reverse magnetic domains are difficult to form. From the above considerations, it has become clear that thin film soft magnetic materials have problems specific to thin films, and that it is therefore difficult to achieve both μm characteristics and μmax characteristics.

By laminating an amorphous soft magnetic film and a crystalline soft magnetic film, the present invention has a large μm of 9 μma, which cannot be achieved with each film alone! It is something that acquires characteristics.

μm1μma according to the present invention! Examples of characteristics are shown in Figures 6 and 7, respectively. The vertical axes are arbitrary scales, and the horizontal axes indicate frequencies. The sample is c in a 1μ pot.

-z r -N b A sendust film with a thickness of 1 μm was formed by sputtering on the fig. Figures 3 and 4
As is clear from the comparison with the figure, both of μm and 1 μmaX exhibit good characteristics.

Although the above example is an example in which a single layer of amorphous material and a single layer of crystalline material are laminated, a structure in which amorphous and crystalline materials are laminated multiple times is also possible.

Further, depending on the surface condition M of the magnetic film, interaction may occur between the laminated films and deteriorate the magnetic properties, so a structure in which a nonmagnetic layer is provided between each magnetic layer is also possible.

[Brief explanation of drawings]

Figure 81 shows the frequency dependence of magnetic loss. The vertical axis shows loss, and the horizontal axis shows frequency. FIG. 2 shows the dependence of magnetic loss on magnetic flux density. The vertical axis represents loss, and the horizontal axis represents magnetic flux density. FIGS. 3 and 4 show the frequency dependence of the initial magnetic permeability μ and the maximum magnetic permeability μmaX of amorphous and crystalline soft magnetic materials, respectively. The vertical axes are μm in FIG. 3 and μmfLX in FIG. 4, which are arbitrary scales, and the horizontal axes are frequencies. Figure 5 shows amorphous ■Oo -F a -B i -
B, ■F e -N i -B i -B, and crystalline soft magnetic material, ■! The dependence of the number of domain walls on magnetic flux density for 1% B i -Fe is shown. The vertical axis represents the number of domain walls, 5, and the horizontal axis represents the magnetic flux density. FIGS. 6 and 7 show the frequency dependence of μm 1 μmax of a film in which sendust, which is an amorphous Oo-Zr-Nb film, is laminated as an example according to the present invention. The vertical axis is μm in FIG. 6 and μmax in FIG. 7, and each is an arbitrary scale. Also, the horizontal axis is frequency. Applicant Suwa Seikosha Co., Ltd. Agent Patent Attorney Mogami Tsutomu (1'/, A'') JL (4-1 YO (?lz) /ρ2 /ρI lσ' B 4-cho) frCHX) Figure 4 102/θ4 /θ6 'rc)-1yr Figure 6

Claims (1)

[Claims] 1. A soft magnetic thin film characterized by laminating one or more crystalline soft magnetic thin films and one or more amorphous soft magnetic thin films. 2. The soft magnetic thin film according to claim 1, characterized in that a nonmagnetic layer is provided between the magnetic films.