Dynamic magnetic information storage or retrieval – Monitoring or testing the progress of recording
Reexamination Certificate
1998-12-22
2001-09-25
Neal, Regina Y. (Department: 2651)
Dynamic magnetic information storage or retrieval
Monitoring or testing the progress of recording
C360S053000, C360S066000, C360S077080, C360S313000, C360S324100
Reexamination Certificate
active
06295175
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a storage apparatus such as a magnetic disk apparatus using a spin valve head as a read head integrated with a write head, and more particularly to a storage apparatus using a spin valve head through which a sense current flows in the interference direction generating a magnetic field opposite in direction to a magnetic field in a pin layer.
2. Description of the Related Arts
With the increased capacitance of the magnetic disk apparatus, the recording density on a magnetic disk medium has become further improved. Such a high recording density that exceeds 3 Gbit/inch
2
is making it difficult to use as an apparatus due to the lowering in the regenerative signal level and the degradation in the SN ratio. Thus, in order to achieve such a high recording density that exceeds 3 Gbit/inch
2
, the spin valve head has been put to practical use. The spin valve head basically has a four-layered structure consisting of an antiferromagnetic layer, a pin layer, a nonmagnetic layer and a free layer. This structure allows the direction of magnetization in the pin layer in contact with the antiferromagnetic layer to be fixed and prevents the free layer separated by the nonmagnetic layer from having a fixed direction of magnetization. When an external magnetic field is applied thereto in the form of a record magnetic field of the medium, the direction of the magnetic field of the free layer is determined by the external magnetic field, and a resistance value varies depending on the difference relative to the direction of the magnetic field of the pin layer. This resistance value is maximized when the directions of the magnetic field in the free layer and the pin layer are opposite 180 degrees to each other, and is minimized when they are identical. Furthermore, the spin valve head allows a sense current to flow therethrough in order to cancel an unnecessary vertical bias magnetic field which may be applied to the free layer as a result of a magnetic coupling of the pin layer which could be called a permanent magnet from its effective aspect. The direction in which the sense current flows includes two directions, that is, an assist direction generating a magnetic field in the same direction as the pin layer, and an interference direction generating a magnetic field opposite to the pin layer. Typically, the interference direction results in a larger output and smaller vertical asymmetry.
In the case of the spin valve head through which the sense current flows in the interference direction, however, a magnetic field by the sense current is generated in the opposite direction to the magnetic field in the layer, so that there arises a problem that the direction of the magnetic field in the pin layer may be offset if the temperature of the antiferromagnetic layer exceeds the blocking temperature due to the external temperature, heating of the element, static electricity, etc. In case the antiferromagnetic layer is made of FeMn in particular, the blocking temperature is as low as 150° C., which may cause a serious problem. In the assist direction, on the other hand, the direction of the magnetic field in the pin layer is the same as the direction of the magnetic field generated by the sense current, so that any offset of the magnetic field in the pin layer is hard to occur.
SUMMARY OF THE INVENTION
It is therefore the object of the present invention to provide a storage apparatus ensuring a normal action even though an offset of the direction of the magnetic field has occurred in a pin layer of a spin valve head through which a sense current flows in the interference direction.
The present invention is directed to a storage apparatus provided with a plurality of heads each having a read head and a write head which have been integrated thereinto, the read head comprising a spin valve head having a multilayered structure including an antiferromagnetic layer, a pin layer, a nonmagnetic layer and a free layer, the spin valve head electrically reading record information from a variation in the magnetic reluctance in response to a record magnetic field of a medium applied in the form of an external magnetic field with a sense current being allowed to flow therethrough in the interference direction causing a magnetic field opposite to the magnetic field in the pin layer. Such a storage apparatus using as the read head the spin valve head through which a sense current flows in the interference direction is characterized in that in the present invention it comprises a pin layer magnetic field offset judgment unit which, when there is judged a predetermined abnormality attributable to a magnetic field offset in the pin layer of the spin valve head, inverts the direction of the sense current and consequently if the predetermined abnormality is eliminated, judges that an offset of the magnetic field has occurred in the pin layer; and a recovery processing unit which, when the pin layer magnetic field offset judgment unit has judged that an offset of the magnetic field in the pin layer has occurred, allows a recovery from the abnormality arising from the offset in the magnetic field. That is, the present invention gives attention to the fact that when a sense current in the interference direction flows through the spin valve head, any possible offset of the direction of the magnetic field in the pin layer may cause an inversion of the polarity of the head read signal, a decrease of the amplitude of the head output as well as an enlarged vertical asymmetry, to thereby judge whether the direction of the magnetic field in the pin layer is normal or not. If an abnormality has been judged, the sense current is inverted, and consequently if the abnormality has been eliminated, a magnetic field offset in the pin layer is judged to perform recovery processing for modifying the direction of the magnetic field in the pin layer. By having a function for detecting an offset of the magnetic field in the pin layer which may be caused by some reason and modifying the direction of the magnetic field in the pin layer in this manner, a stable action is assured with the sense current in the interference direction flowing through the spin valve head, to contribute to an improvement in the reliability of the apparatus.
For example the pin layer magnetic field offset judgment unit, when servo marks recorded on said record medium can be detected no longer, may judge that there has occurred an abnormality attributable to a magnetic field offset in the pin layer, and may invert the direction of the sense current and consequently if it has become possible to detect the servo marks, judge that an offset of the magnetic field has occurred in the pin layer. The recovery processing unit when it has become possible to detect the servo marks as a result of switching of the direction of the sense current from the interference direction to the assist direction, allows the sense current to flow through the spin valve head in the assist direction upon the reading action. To this end, the recovery processing unit when the direction of the sense current has been switched to the assist direction as a result of occurrence of an offset of the magnetic field in the pin layer, stores into a nonvolatile memory that the direction of the sense current is the assist direction in a manner corresponding to head numbers, the recovery processing unit determining the direction of the sense current upon the reading action on the basis of the content of record of the nonvolatile memory. The recovery processing unit when the direction of the sense current has been switched to the assist direction, allows upon the reading action the sense current to flow with a larger current value than the current value in the interference direction before switching. This is due to the necessity to compensate for the read signal level in the assist direction lower at the same current value than that in the interference direction. The pin layer magnetic field offset judgment unit may comp
Hoshino Toshinori
Kanai Hitoshi
Koshikawa Takao
Nakamura Tadashi
Tomita Isamu
Fujitsu Limited
Greer Burns & Crain Ltd.
Neal Regina Y.
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