High resistance magnetic film

Details High resistance magnetic film High resistance magnetic film

2000-01-18

2002-04-30

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

Composite

Of metal

C428S432000, C428S450000, C428S704000, C428S900000, C148S306000, C148S310000, C252S062560, C252S062570, C252S062590, C252S062620, C252S062630

Reexamination Certificate

active

06379810

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high resistance magnetic film used in magnetic application components such as a magnetic recording head, a magnetic reproduction head, a magnetic sensor including a magnetic impedance sensor, a magnetic coil, an inductor, a transformer, and a magnetic shield.
2. Description of the Prior Art
In recent years, the need for high frequency magnetic devices is high, and magnetic materials having excellent soft magnetic characteristics at a frequency of 100 MHz or more are required. A magnetic material used at such a high frequency requires a loss mainly due to eddy current and ferromagnetic resonance to be small. In other words, from the aspect of material properties, mainly high electrical resistivity or high saturation magnetic flux density are required.
Conventionally, Japanese Laid-Open Patent Publication No. (Tokkai-Hei) No. 4-21739 proposed a composite material obtained by forming an oxide on surfaces of magnetic metal particles and sintering it in order to achieve high saturation magnetic flux density of about 1 T or more. As the oxide, Japanese Laid-Open Patent Publication No. (Tokkai-Hei) No. 6-120020 proposed Mg—O, Ca—O, Si—O, Al—O, Ti—O or the like.
On the other hand, research as to FeNbCuSiB or the like reported in Japan Metal Association Journal 53 (1989) 241 shows that the soft magnetic characteristics can be improved by miniaturizing the size of magnetic crystal grains constituting a magnetic body to about 20 nm or less. Furthermore, Japanese Laid-Open Patent Publication No. (Tokkai-Hei) No. 7-86035 proposed a FeM′NO (M′=Be, Mg, Al, Si, Ca, etc.) material formed by sputtering as a material having both improved soft magnetic characteristics and high saturation magnetic flux density, which are achieved by using the composite material and effecting such a high level of miniaturization.
The conventional FeM′NO material proposed in the related art is produced by two-phase separation into Fe microcrystals having a bcc crystal structure and a M′O or M′N compound forming the grain boundary thereof by selective oxidation or selective nitriding of a M′ element caused by a difference in the free energy of oxide or nitride formation between Fe and M′ elements that are forming the film during sputtering.
However, sputtering is a technique that degrades a target element to an atomic or molecular level and effects synthesis on a substrate. In addition, it is substantially difficult to effect complete two-phase separation of the elements only by the energy during sputtering. Therefore, it is inevitable that a Fe microcrystal of the FeM′NO material is in the form of a solid solution with an O, N or M′ element immediately after the formation of the film. For this reason, even if microcrystals having Fe as a main component maintain a bcc structure, the magnetostriction constant of the material becomes as large as 1×10
−5
or more, or the crystal magnetic anisotropy energy of Fe becomes large. Thus, the soft magnetic characteristics deteriorate. Therefore, in the case where these materials are to be produced for industrial applications, it is difficult to control the magnetostriction to be low and the soft magnetic characteristics to be high in a large area due to even a small discrepancy in the composition or the like.
The above described points were made evident as a result of the study of the inventors of the present invention on magnetic films such as FeSiO, FeMgO or the like.
The two-phase separation can proceed further by raising the substrate temperature during formation of a FeM′NO film or performing a heat treatment after the film is formed. However, since the temperatures for these heat treatments are generally 400° C. or more, the soft magnetic characteristics deteriorate due to large crystal grains, or the film cannot be used in a device that requires a low temperature process at a temperature lower than that temperature. Moreover, in general, it is known that the optimum relationship between the saturation magnetic flux density and the electric resistivity is different between magnetic devices, even the same types of devices, depending on the size, the frequency used or the like. Nevertheless, conventionally, a method for optimum adjustment of these characteristics is not known.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is an object of the present invention to provide a magnetic film that has high resistance, low magnetostriction and high soft magnetic characteristics, and is excellent in practical aspects such as adjustment of the characteristics.
In order to achieve the above object, the magnetic film of the present invention is expressed by a composition formula T
a
M
b
X
c
N
d
O
e
(where a, b, c, d and e represent at. % and are values satisfying the following equations, T is (1) Fe or (2) a metal comprising not less than 30 at. % of Fe and at least one selected from the group consisting of Co and Ni, M is at least one selected from the group consisting of Be, Mg, Ca, Sr and Ba, and X is at least one selected from the group consisting of Y, Ti, Zr, Hf, V, Nb, Ta and lanthanoid). The magnetic film comprises mainly metal magnetic crystal grains having an average crystal grain diameter of not more than 15 nm and a grain boundary product. The main component of the metal magnetic crystal grains is the T. The grain boundary product contains at least an oxide or a nitride of the M and the X. The magnetic film has a saturation magnetic flux density of not less than 0.8 T and an electric resistivity of not less than 80 &mgr;&OHgr;cm.
a+b+c+d+e=
100
45
≦a
≦85,
5.5
≦b
≦28,
0.5
≦c
≦16,
6≦
b+c≦
28.5,
0.4
<b/c
≦56,
0≦
d≦
10,
and
8
≦d+e
≦40.
Lanthanoid specifically refers to La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb and Lu. It is preferable that the grain boundary product substantially separates the metal magnetic crystal grains. In this specification, “main component” means a component included in an amount more than 50 atomic %, preferably more than 70 atomic %. The magnetic film of the present invention can contain impurities of inert elements such as Ne, Ar, Kr, Xe or the like in an amount not more than 1 atomic %. If the impurities are C, B, F, S, P or the like, the magnetic film of the present invention can contain them in an amount not more than 5 atomic %.
Throughout the description below, % for a composition ratio means atom %.
M and X are relatively hard to form a solid solution with T. Both of the elements are characterized by having a smaller free energy for oxide or nitride formation than that of T. Among them, M tends to have a large free energy for oxide formation, and an X element tends to have a large free energy for nitride formation. When a film is produced in the above composition range, since M or X that forms a solid solution in the metal magnetic crystal grains is present only in a small amount, an increase of the magnetostriction and the crystal magnetic anisotropy energy due to the solid solution of the elements is relatively small in the obtained magnetic film. Moreover, M or X forms an oxide or nitride so as to suppress grain growth mainly of magnetic crystal grains or form a grain boundary having a high resistance.
In this case, in the present invention, combination ratios of M or X and oxygen and nitrogen are selected as those described above. As a result, the width of the grain boundary or the coating ratio of magnetic crystal grains can be controlled, so that the saturation magnetic flux density and the electric resistivity can be selected arbitrarily from wide ranges as well as the soft magnetic characteristics.
M, which is an alkaline earth metal, generally is quite reactive, so that it is preferable that it is used in the form of a stable compound for industrial handling. For example, in the case where M is Ca, it is more convenient to be in the form of CaO for handling,

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