Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-10-05
2003-08-05
Miller, Brian E. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06603643
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording/reproducing apparatus and a magnetoresistive element, and more particularly to a high-density magnetic recording/reproducing apparatus and a method of manufacturing the same.
JP-A-9-16920 describes a spin-valve magnetoresistive sensor using a laminated antiparallel pinned layer and an antiferromagnetic exchange bias layer.
JP-A-7-169026 describes a spin-valve sensor using an antiferromagnetic coupling layer.
JP-A-6-236527 describes a magnetoresistive sensor having a conductive back layer at the back of a filter layer responsive to a magnetic field.
JP-A-6-111252 describes a magnetoresistive sensor having a soft-magnetic intermediate layer adhered between an antiferromagnetic layer and a ferromagnetic layer.
U.S. Pat. No. 5,768,071 describes a spin-valve type read head, in which exchange coupling is improved by inserting a thin, non-contiguous nonmagnetic layer of, for example, Cu between an antiferromagnetic film and a ferromagnetic film.
JP-A-2000-156530 describes a magnetoresistive element including a third layer of, e.g., oxide in a second magnetic layer with magnetization substantially fixed. Further, the Society of Japan Applied Magnetism, Summary Proceedings of 23rd Conference 6aA-5, describes a spin-valve film having a magnetization fixed layer containing a nano oxide layer.
Digests of Intermag 2000, FA-08, describes a giant magnetoresistance (GMR) film making use of a thin oxide. FA-07 of the same literature describes a GMR film having a protective oxide film laminated on a free layer. BQ-12 of the same literature also describes a GMR film having a protective oxide film laminated on a free layer. FA-09 of the same literature describes a spin-valve film using a magnetic oxide layer.
Digests of Intermag 1999, DB-01, describes a spin-valve film making use of a pinned layer having an oxide layer inserted therein.
Physical Review B53, 9108 (1996) and Journal of Applied Physics, 79, 5277 (1990) describe that the giant magnetoresistance is enhanced by an effect of an interface with an oxide.
In the prior art, it has been impossible to realize a magnetic recording apparatus with a sufficiently high recording density, in particular, magnetoresistive elements in a read unit of the apparatus, which act on the external magnetic field with adequate sensitivity and output, and further to obtain a favorable performance with good symmetry, so that it has been difficult to realize the function as a storage device.
In recent years, it has been known that a multi-layer film having ferromagnetic metal layers laminated with nonmagnetic metal layers therebetween is great in magnetoresistance, or a so-called giant magnetoresistance. In this case, the magnetoresistance is varied in electric resistance in accordance with an angle formed by magnetizations of the ferromagnetic layers separated from one another by the nonmagnetic layers. In the case of using the giant magnetoresistance for magnetoresistive elements, a structure called a spin valve has been proposed. More specifically, output can be obtained by providing a structure of antiferromagnetic film/ferromagnetic layer
onmagnetic layer/soft-magnetic layer, using an exchange coupling magnetic field generated at the interface of antiferromagnetic film/ferromagnetic layer to substantially pin magnetization of the ferromagnetic layers in close contact with the antiferromagnetic films, and causing an external magnetic field to perform magnetizing rotation of the other soft-magnetic layer. The effect of the above pinning is called a pinning bias, and the antiferromagnetic film producing such effect is called a pinning bias film. Also, that ferromagnetic layer, for which the magnetization is substantially pinned, is called a pinned layer or a ferromagnetic pinned layer. Similarly, a soft-magnetic film caused by an external field to undergo rotation of magnetization is called a free layer or a soft-magnetic free layer. The pinned layer functions to be substantially pinned in magnetization relative to a magnetic field being sensed, and the antiferromagnetic film can be replaced by a hard magnetic film, that is, a material, for which magnetization will not change except for application of a relatively large magnetic field.
With a magnetic head using the spin-valve type magnetoresistive laminated film, important factors include a thickness of the pinned layer and an amount of its magnetization. That is, this is because with a magnetic head having opposite surfaces exposed, a magnetic field leaks from ends of pinned layers in accordance with an amount of magnetization of pinned layers, i.e., a product of magnetization and thickness as one of factors of symmetry in waveform of a read head relative to an external field to have an influence on a direction of magnetization of free layers. In keeping with an increased recording density of magnetic recording/reproducing apparatuses in recent years, spin-valve sensors serving as read elements have been increasingly made small in size and leakage of the magnetic field from ends of pinned layers has produced large influences. To cope with this, it is necessary to reduce an amount of magnetization of pinned layers, i.e., reduce pinned layers in thickness or magnetic flux density. Simply thinning of pinned layers in a spin-valve laminated film, however, magnifies the effect of surface scattering to cause reduction in MR ratio, which will in turn impair the performance of a read sensor. Similarly, when the pinned layers of a spin-valve laminated film are modified in composition so as to be reduced in magnetic flux density, the giant magnetoresistance is impaired to cause reduction in MR ratio, which will also impair the performance of a read sensor. These problems are also observed with the free layer. JP-A-6-236527 proposes a construction, in which a conductive layer is provided behind a free layer called a filter layer to suppress reduction in MR ratio due to the surface scattering effect. Also, Physical Review and Journal of Applied Physics have pointed out that the effect of oxide causes an improvement in giant magnetoresistance. Further, the summary proceedings of conference of the Society of Japan Applied Magnetism has reported that a spin-valve film with oxide layers formed in pinned layers is high in MR ratio.
When an oxide and an antiparallel coupling layer are inserted in a pinned layer so as to apply a spin-valve type magnetoresistive laminated film to a magnetic head, in particular to a magnetic head for magnetic recording/reproducing apparatuses of high recording density, however, it is easily expected that a pinned layer will be of complex construction consisting of at least three of the magnetic films and oxide films and further five or more layers consisting of antiparallel coupling layers laminated. Such complex structure of a pinned layer can be an obstacle to attaining the function of a magnetoresistive element and makes it difficult to induce and produce a pinning bias essential for the operation of a spin-valve structure. For the magnetic head to function, a pinning bias is applied in a predetermined direction as described above. That is, a pinning bias is applied in a predetermined direction described above upon functioning as a magnetic head. A method of manufacturing a magnetic head comprises applying a magnetic field to a magnetoresistive film and performing heat treatment in a state, in which magnetization of a magnetic film in contact with an antiferromagnetic film is saturated in a predetermined direction described above, to apply a pinning bias. However, since the pinned layer is of complex structure and contains therein an antiparallel coupling layer having the property of firmly maintaining the magnetized state of an adjacent magnetic film in an antiparallel direction, a necessary performance cannot be obtained even when a magnetoresistive element is formed only by combining conventional techniques.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a magnet
Hoshiya Hiroyuki
Imagawa Takao
Meguro Kenichi
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Miller Brian E.
Watko Julie Anne
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