Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1998-04-24
2002-10-22
Hudspeth, David (Department: 2754)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06469873
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
This invention relates to a magnetic storage apparatus used for computers and information processing apparatuses, and more particularly relates to a magnetic head and a magnetic storage apparatus suitable for a perpendicular magnetic recording medium obtained realizing a high density recording.
2. Description of the prior art
Information processing apparatus employs mainly semiconductor memory and magnetic memory as their storage apparatus. Semiconductor memory is used mainly for the internal storage apparatus in view of access time , and magnetic memory is used mainly for external storage apparatus in view of large capacity and non-volatility.
Recently, magnetic disk and magnetic tape have been mainly used as magnetic memory. A recording medium used for these magnetic memory comprises an Al substrate or resin tape on which a magnetic thin film is formed. To record magnetic information on the recording medium, a functional component having electromagnetic conversion function is used. To reproduce magnetic information, a functional component which utilizes magnetoresistive phenomenon, giant magnetoresistive phenomenon, or electromagnetic induction phenomenon is used. The functional component is incorporated in an input/output unit so-called a magnetic head.
A magnetic head and a recording medium are moved relative to one another, and have a function to record magnetic information on the arbitrary position of the medium and to reproduce electrically magnetic information as required.
As shown in
FIG. 2
, a magnetic head comprises , for example, a recording component
21
for recording magnetic information and a reproducing component
22
for reproducing magnetic information.
The recording component
21
comprises a coil
26
and magnetically coupled magnetic poles
27
and
28
located so that the coil
26
is sandwiched therebetween.
The reproducing component
22
comprises a magnetoresistive effect unit
23
and a pair of an electrode
29
for supplying a constant current to the magnetoresistive effect unit
23
and for detecting resistance change.
Between the recording component
21
and the reproducing component
22
, a magnetic shield layer
28
(served also as the write pole) is provided. These functional components are formed on a magnetic head body
30
through a primary layer
24
and shield layer
25
.
The example shown in
FIG. 2
utilizes electromagnetic conversion function for recording and utilizes magnetoresistive effect for reproducing. However, the reproduction of magnetic information may be performed by detecting electromagnetic induction current induced in a coil provided in a recording component. In this case one component is served for both recording and reproducing.
The performance of a storage apparatus depends on the input/output operation speed and storage capacity, as a result, short access time and large storage capacity are essential to render the product competitive. Recently small sized storage apparatus have been developed in response to the request for compact information apparatus. To satisfy this request, development of a magnetic memory device for recording and reproducing much magnetic information in and from a single sheet of recording medium is important.
To satisfy this request, it is required to increase the recording density of a magnetic memory device. To increase the recording density, it is required to miniaturize the size of domain which is the source of magnetic information. It is also required to increase the frequency of recording current supplied to the coil
26
shown in FIG.
2
and to narrow the design of the width W of recording magnetic pole
27
.
According to the examination performed by the inventors, a recording pole width W of 2.5 &mgr;m and a recording frequency of about 90 MHz realized a recording density of 2Gb/in
2
class. However, it was found that an even higher density caused a problem and revealed the limitation of high density recording.
Heretofore, magnetic films called longitudinal media of in-plane magnetization direction have been used as recording media. In an in-plane medium, the boundary between domains is mainly magnetized, and the magnetization is read out by detecting field intensity. Because the magnetization is concentrated, a signal of Gaussian shape (Lorentzian shape) pulse signal is outputted. Since the frequency band contained in a signal is narrow, it is less susceptible to the deterioration of signal quality due to neighboring signal. Therefore, signals are processed easily thereafter.
However, thermal fluctuations of magnetization is an inevitable problem in development of high density recording using an in-plane medium. The thermal fluctuations are due to thermal fluctuations of magnetization in a recording medium, and the thermal fluctuations are caused by increasing miniaturization of domains because the demagnetizing effect of neighboring domains become remarkable and the magnetization direction becomes unstable.
According to experiments conducted by the inventors, it was confirmed that domains could be erased due to thermal fluctuation when density was increased as high as to about 400 kbPI (bits per inch) in the circular direction and about 26 kTPI (tracks per inch) in the radius direction.
The perpendicular magnetic recording is known as a technology for preventing the problem. Because demagnetization of neighboring domains function so that fluctuations width of magnetization due to thermal fluctuation are decreased, the domain erasing phenomenon due to thermal fluctuation is less susceptible. Therefore, the perpendicular magnetic recording is expected to be the high density recording technology of the future.
However, because magnetic charges are distributed on the medium surface in the perpendicular magnetic recording, if magnetization is reproduced using a reproducer used for detecting field intensity of a conventional longitudinal medium as shown in
FIG. 2
, square wave (dipulse) is detected depending on domain width. Such a square wave requires complex signal processing because of wide band. Such complex signal processing requires use of a complex electric circuit. Therefore, it is difficult to realize an inexpensive and high speed apparatus, and as a result, this problem is one of the reasons for slow commercialization of perpendicular magnetic recording.
SUMMARY OF THE INVENTION
The above-mentioned problem will be solved if output signals obtained from perpendicular media are of Gaussian shape similar to conventional longitudinal media.
Accordingly, it is the object of the present invention to provide a magnetic head and a magnetic recording apparatus using the magnetic head having a novel reproducing means which is capable of outputting reproducing signal obtained from a perpendicular magnetic medium as a Gaussian shape pulse signal. The present invention realizes a high speed and high density magnetic recording apparatus which utilizes a perpendicular magnetic recording method.
In order to realize the above-mentioned object, the magnetic head and the magnetic recording apparatus using the magnetic head of the present invention use means described hereinafter.
The first embodiment uses a perpendicular magnetization film having an easy magnetization axis perpendicular to the direction of the film surface, and the first embodiment is provided with at least a magnetic head having a function for recording and reproducing information. Particularly in the magnetic head, a reproducing means for having reproducing function of information is provided with piled up or stacked two spin valve elements with a pinned layers having magnetization direction difference of about 180 degrees, and recorded information is reproduced from the perpendicular magnetization film.
In detail, the object of the present invention is accomplished by providing a magnetic recording apparatus provided with a perpendicular magnetic recording medium having an easy magnetization axis in the direction perpendicular to the longitudinal surface, and a magnetic head
Maruyama Yoji
Nakatani Ryoichi
Suzuki Yoshio
Takano Hisashi
Castro Angel
Hitachi , Ltd.
Kenyon & Kenyon
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