Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Reexamination Certificate
1994-01-06
2001-02-06
Resan, Stevan A. (Department: 1773)
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
C148S122000, C148S306000, C148S318000, C427S130000, C428S692100, C428S704000
Reexamination Certificate
active
06183568
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a soft magnetic thin film having high saturation magnetic flux density and magnetic permeability at higher frequencies and advantageously employed, e.g., as a core material for a magnetic head adapted for high density recording and/or reproduction, a method for producing the same, and a magnetic head for high density recording and/or reproduction wherein use is made of soft magnetic layers exhibiting a high saturation magnetic flux density and a high frequency magnetic permeability as the core material for the magnetic head.
The present invention further relates to a magnetic head for high density recording and/or reproduction having a diffusion inhibiting layer between a ferrite core and a particular soft magnetic layer.
BACKGROUND OF THE INVENTION
In the field of magnetic recording and/or reproducing apparatus, such as audio tape recorder or a video tape recorder (VTR), for example, the general tendency is towards a higher recording density and a higher quality of recording signals. In keeping with this tendency towards the higher recording density, a so-called metal tape in which powders of metals such as Fe, Co or Ni, or alloys thereof, are used as the magnetic powders, or a so-called vacuum-deposited tape in which a magnetic metal material is directly deposited on a base film by the thin film forming vacuum technique, has been developed and put to practical use in many technical fields.
Prior Art and Problem to be Solved
Meanwhile, if the characteristics of the magnetic recording medium having a predetermined coercive force is to be displayed fully, it is required of the core material for the magnetic head to exhibit a higher saturation magnetic flux density as its magnetic properties or characteristics. In addition, if reproduction is to be achieved with the same magnetic head as that used for recording, it is also required of the core material to exhibit a higher magnetic permeability.
Although the Sendust alloy (Fe—Si—Al, Bs about equal to 10 KG) or a Co-base amorphous alloy has so far been used, it is difficult with the Sendust alloy to increase the film thickness because of the larger inner stress imposed on the film and the difficulty in making a thick film due to the susceptibility of the film to growth of the crystal grains. Also the Sendust alloy has the saturation magnetic flux density Bs of about 10 KG, which however falls short in view of the tendency towards an increasing higher recording density. On the other hand, while the Co-base amorphous alloy has satisfactory magnetic properties and may be fabricated with a high saturation magnetic flux density Bs, it has a drawback that, since it is crystallized at 450° C. or thereabouts, it cannot be glass bonded at elevated temperatures for preparing the magnetic head, such that it is not possible to develop a high enough bonding strength.
Among other soft magnetic materials is iron nitride, which is usually formed into a thin film by ion beam vacuum deposition or sputtering in a nitrogen-containing atomosphere, using iron as the target. However, the soft magnetic thin film of iron nitride has a drawback that the coercive force is markedly increased due to heating upon glass bonding and the magnetic properties thereof are inferior in stability.
In the JP Patent KOKAI 63-299219 (1988), there is disclosed a soft magnetic thin film which is aimed at obtaining the above mentioned drawback and which is represented by the formula Fe
x
N
y
A
z
wherein x, y and z each denote the compositional ratios in atomic percent and A denotes at least one of Si, Al, Ta, B, Mg, Ca, Sr, Ba, Cr, Mn, Zr, Nb, Ti, Mo, V, W, Hf, Ga, Ge and rare earth elements, and wherein the compositional ratios are such that
0.5≦y≦5.0
0.5≦z≦7.5 and
x+y+z=100.
However, it is not preferred to use the soft magnetic thin film described in the JP Patent KOKAI 63-299219 (1988) in preparing a magnetic head by a process including the heating step, such as a glass bonding step, because its coercive force is inevitably increased on heating.
The above film has also a drawback that, because it does not assure uniaxial anisotropy, its magnetic permeability cannot be increased at higher frequencies.
Also, the crystal materials in general tend to be turned into columnar crystals, during the film depositing process, due to the self-shadowing effect, depending on the film forming conditions, so that voids tend to be formed in the grain boundary region resulting in magnetic discontinuity and inferior soft magnetic properties. These self-shadowing effect becomes particularly outstanding when there is a step-like surface irregularity on the underlayer or substrate as in the case of preparation of the magnetic head, or when a thicker film is to be produced, so that sufficient magnetic properties cannot be obtained.
The soft magnetic thin film disclosed in the above prior art publication is not desirable as the magnetic head core material in view of the above mentioned drawbacks.
It is an object of the present invention to provide a novel soft magnetic thin film, a novel method for preparing a soft magnetic thin film and a novel magnetic head, which are free from the above-mentioned problems of the conventional art.
According to the present invention, the above object may be accomplished by a soft magnetic film, a method for producing the soft magnetic film and a magnetic head, which may be summarized in the following manner.
First Aspect:
There is provided a soft magnetic thin film represented by the compositional formula Fe
a
T
b
N
c
wherein the a, b and c each stand for atomic percent and T stands for at least one of Zr, Hf, Ti, Nb, Ta, V, Mo or W and wherein the composition is in the range of
0<b≦20 and
0<c≦22
with the exclusion of the range defined by b≦7.5 and c≦5. Such compositional range is defined by a line conecting points E, F, G, H, I and J in
FIG. 1
(referred to as “EFGHIJ composition” hereinafter).
As will become clear hereinafter, this soft magnetic thin film has a saturation magnetic flux density markedly higher than that of the Sendust alloy or the amorphous soft magnetic alloys and can provide a preferred embodiment with a zero magnetostriction to enable excellent soft magnetic properties such as the low coercive force and high magnetic permeability.
On the other hand, the soft magnetic thin film of the present Aspect has an electrical resistivity as high as that of Sendust and may be subjected to heat treatment in the magnetic field to develop uniaxial anisotropy, the magnitude of which can be controlled depending on the composition of the thin film and the duration of heat treatment to realize the high magnetic permeability at higher frequencies meeting requirements of the intended use and application. The thin film of the present Aspect has superior thermal resistance against the glass bonding since its characteristics are not deteriorated by heat treatment up to 650° C. The thin film of the present Aspect also has high hardness and corrosion resistance and hence a high abrasion resistance, in the all, turning out to be a highly reliable material.
The soft magnetic thin film of the present invention exhibits satisfactory step coverage in film formation since the film material can be formed as an amorphous alloy for preparaing a film and can be subsequently heat-treated so as to be turned into a microcrystalline state. In addition, a mirror surface can be easily developed, while the crystal grains can be inhibited from coarsening (excessive grain growth) without the necessity of resorting to a multilayered structure so that a film of a larger thickness (thick film) may be produced.
Thus the soft magnetic thin film of the present Aspect may be employed as the core material for a magnetic head to cope with the high coercivity magnetic recording medium to realize high quality and bandwidth as well as high recording density.
Second Aspect:
There is provided a method for producing a soft magnetic thin film comprising the steps:
forming an amorphous alloy film of th
Isomura Tatsuya
Katayama Masaaki
Nakanishi Kanji
Shimizu Osamu
Yoshida Satoshi
Fuji Photo Film Co. , Ltd.
Resan Stevan A.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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