Magnetoresistance effect type head

Details Magnetoresistance effect type head Magnetoresistance effect type head

2000-02-29

2003-05-20

Cao, Allen (Department: 2652)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

Reexamination Certificate

active

06567247

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetoresistance effect type head for reading the magnetic field intensity of a magnetic recording medium or the like as a signal and, in particular, to a magnetoresistance effect type head using a spin valve film structure as a substantial magnetic information reading means.
2. Description of the Related Art
Recently, there has been the development for increasing the sensitivity of magnetic sensors and increasing the density in magnetic recording and, following this, magnetoresistance effect type magnetic sensors (hereinafter referred to as MR sensors) and magnetoresistance effect type magnetic heads (hereinafter referred to as MR heads) using magnetoresistance change have been actively developed. Both MR sensors and MR heads are designed to read out external magnetic field signals on the basis of the variation in resistance of a reading sensor portion formed of magnetic material. The MR sensors have an advantage that a high sensitivity can be obtained and the MR heads have an advantage that a high output can be obtained upon reading out signals magnetically recorded in high density because the reproduced output does not depend on the relative speed of the sensors or heads to the recording medium.
However, conventional MR sensors which are formed of magnetic materials such as Ni
80
Fe
20
(Permalloy), NiCo or the like have a small resistance change ratio &Dgr;R/R which is about 1 to 3% at maximum, and thus these materials have insufficient sensitivity as the reading MR head materials for ultrahigh density recording of the order of several GBPSI (Giga Bits Per Square Inches) or more.
Attention has been recently paid to artificial lattices having the structure in which thin films of metal having a thickness of an atomic diameter order are periodically stacked, because their behavior is different from that of bulk metal. One of such artificial lattices is a magnetic multilayered film having ferromagnetic metal thin films and non-magnetic metal thin films alternately deposited on a substrate. Heretofore, magnetic multilayered films of an iron-chromium type, a cobalt-copper type and the like have been known. However, these artificial lattice magnetic multilayered films are not commercially applicable as they are because the external magnetic field at which a maximum resistance change occurs (operating magnetic field intensity), is as high as several tens of kilo-oersted.
Under these circumstances, a new structure which is called a spin valve has been proposed. In this structure, two NiFe layers are formed via a non-magnetic metal layer, and an FeMn layer, for example, is further formed as a pinning layer so as to be adjacent to one of the NiFe layers.
In this case, since the FeMn layer and the NiFe layer adjacent thereto are directly exchange-coupled to each other, the direction of the magnetic spin of this NiFe layer is fixed in the range of several tens to several hundreds Oe in magnetic field intensity. On the other hand, the direction of the magnetic spin of the other NiFe layer is freely changeable by an external magnetic field. As a result, there can be achieved a magnetoresistance change ratio (MR ratio) of 2 to 5% in a small magnetic field range which corresponds to the degree of coercive force of the NiFe layer.
In the spin valve, by realizing a difference in relative angles of spins between two magnetic layers, the large MR change which differs from the conventional anisotropy magnetoresistance (AMR) effect is accomplished. This is realized by pinning of the magnetic layer spin due to the direct exchange coupling force between one of the magnetic layers and the antiferromagnetic layer. This exchange coupling can be the to be the substance of the spin valve.
As shown in
FIG. 7
being a schematic structural diagram, the conventional general spin valve type magnetoresistance effect type head includes a spin valve film (magnetoresistance effect film) composed of a soft magnetic layer
20
, a non-magnetic metal layer
30
, a ferromagnetic layer
40
and a pinning layer
50
which are stacked in turn on a substrate, and further includes electrode portions
100
provided at both ends of the laminate film via hard magnetic layers (hard magnets)
500
.
The main function of the hard magnetic layers (hard magnets)
500
is as follows: Specifically, a rising portion of the MR curve is determined by the rotation of magnetization of the soft magnetic layer
20
. For obtaining sharper rising of the MR curve, it is desirable that the soft magnetic layer
20
changes its magnetization direction relative to a signal magnetic field solely by the magnetization rotation. However, in practice, the magnetic domain is generated in the soft magnetic layer
20
so that the magnetic wall movement and the magnetization rotation occur concurrently relative to the signal magnetic field. As a result, the Barkhausen noise is generated to render the MR head characteristic unstable. In view of this, the design specification has been adopted wherein by providing the hard magnetic layers (hard magnets)
500
, a bias magnetic field (so-called longitudinal bias magnetic field) is applied in a longitudinal direction (direction of arrow &agr;) of the soft magnetic layer
20
so as to obtain the MR head characteristic with the reduced Barkhausen noise.
However, in the spin valve magnetic head of the type wherein the hard magnetic layers (hard magnets)
500
are provided as a means for applying the foregoing so-called longitudinal bias magnetic field, the following points have been pointed out for improvement: Specifically, because of the magnetostatic field, when a large external magnetic field is applied to the hard magnetic layers (hard magnets), the magnetization direction of the bias magnetic field is liable to be changed due to an influence of the external magnetic field, which has been one cause of an occurrence of noise. There has also been a problem that the produced magnetic field fluctuates due to dispersion of crystal grain sizes of the hard magnetic layers (hard magnets) so that the uniform bias magnetic field can not be applied.
Further, it is difficult for the hard magnetic layers (hard magnets) to efficiently apply the longitudinal bias magnetic field due to the shape thereof to be formed, so that an excessive bias magnetic field may be applied, meaning that further enhancing an output of the magnetic head can not be expected. Moreover, it may also be difficult to realize further narrowing of the track.
The present invention has been made under these circumstances and has an object to provide a magnetoresistance effect type head which can improve an output thereof with reduced noise.
SUMMARY OF THE INVENTION
For solving the foregoing problems, according to one aspect of the present invention, there is provided a magnetoresistance effect type head comprising a magnetoresistance effect film of a spin valve film structure, wherein the magnetoresistance effect film is a spin valve type multilayered film which comprises a non-magnetic metal layer, a ferromagnetic layer formed on one surface of the non-magnetic metal layer, a soft magnetic layer formed on the other surface of the non-magnetic metal layer, and a pinning layer which is formed on a surface of the ferromagnetic layer remote from a surface thereof abutting the non-magnetic metal layer so as to pin a direction of magnetization of the ferromagnetic layer, wherein the soft magnetic layer is set to freely change its magnetization direction in response to an external magnetic field being magnetic information, and soft magnetic bias assist layers are formed at both ends of the soft magnetic layer, respectively, wherein bias applying layers are formed on the soft magnetic bias assist layers in a junction manner, respectively, for applying a bias in a longitudinal direction of the soft magnetic layer, wherein each of the bias applying layers is made of Ru
x
M
y
Mn
z
exhibiting antiferromagnetism, wherein M represents at least one selected from Rh, Pt, Pd, A

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