Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-12-27
2003-12-30
Renner, Craig A. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324110
Reexamination Certificate
active
06671138
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a magnetoresistive effect type of head for detecting intensity of a magnetic field utilizing a resistive change according to the intensity of the magnetic field, and an information-reproducing system for reproducing information stored in a storage medium.
BACKGROUND ART
As computers have come into wide use, a lot of information is dealt routinely recently. Such information is stored in a storage medium with a large number of physical marks, and is reproduced by an information-reproducing system for reading those marks to produce an electric reproduction signal.
A hard disk device (HDD: Hard Disk Drive) is one of such an information-reproducing system and has aspects that it has a large storage capacity and an access time to information is fast. Generally, such a HDD is provided with a magnetic disk of which a surface is a recording medium made of a magnetic material and a reproducing head for reproducing information stored in the magnetic disk. The magnetic disk is magnetized in its surface for each minute area (one-bit area) in which one-bit of information is recorded in the form of a direction of magnetization of the one-bit area. The reproducing head is disposed close to the magnetic disk to output an electric reproduction signal according to a magnetic field generated from the one-bit area of the magnetic disk and thereby reproducing information recorded on the magnetic disk.
Currently, in many of the reproducing heads, which are loaded on the HDD, a signal is sent through a magnetoresistive effect type of head (MR head) which has a magnetoresistive effect element varying a resistance in accordance with an external magnetic field. The magnetoresistive effect element is utilized to generate a high output reproduction signal. However, every year a recording density of a magnetic disk is enhanced, and as the recording density is enhanced, a size of the respective one-bit area of the magnetic disk is reduced, and a magnetic field generated from the magnetization of the one-bit area is weakened. Thus, there is needed a head which outputs a large reproduction signal to such a weakened external magnetic field. As a head that outputs such a large reproduction signal, there is known a spin valve magnetoresistive head (SVMR head). Making the spin valve magnetoresistive head fit for practical use starts in earnest. Hereinafter, the spin valve magnetoresistive head is referred to as an SVMR head.
The SVMR head has a spin valve element consisting of a multi-layer film including a free magnetic layer varying in a direction of magnetization in accordance with an external magnetic field, a non-magnetic metal layer, a fixed magnetic layer fixed in a direction of magnetization, and an antiferromagnetic layer for fixing a direction of magnetization of the fixed magnetic layer. A sensing current conducts through the spin valve element. The spin valve element is one of the above-mentioned magnetoresistive effect elements. In the spin valve element, when the external magnetic field is varied, the free magnetic layer of the spin valve element is varied in a direction of magnetization, and a resistance is varied in accordance with a relative angle variation between a direction of magnetization of the fixed magnetic layer and a direction of magnetization of the free magnetic layer. Generally, efficiency of the resistive change of the magnetoresistive effect element according to the variation of the external magnetic field is expressed by a magnetoresistive rate R
MR
. The magnetoresistive rate R
MR
is defined by R
MR
=(&rgr;
max
−&rgr;
0
)/&rgr;
0
. &rgr;
0
denotes a rate of the magnetoresistive effect element wherein the external magnetic field is not applied. &rgr;
max
denotes the maximum rate of the magnetoresistive effect element wherein the external magnetic field is applied. The spin valve element is large in the magnetoresistive rate, which brings about a large output change through the above-mentioned sensing current. Incidentally, hereinafter, the magnetoresistive rate is referred as MR rate.
As one way of providing higher output of the SVMR head, there is considered a reduction of the height of an element of the spin valve element. Reducing the height of an element of the spin valve element causes a sectional area of a conduction path for the sensing current to be reduced so that the resistive change &rgr;
max
&rgr;
0
becomes large, while the MR rate is not increased. Thus, it is possible to obtain a large output of reproduction signal. However, a direction of magnetization of the fixed magnetic layer points to a direction of height of the spin valve element. Accordingly, a simple reduction of height of the spin valve element causes a demagnetizing field of the fixed magnetic layer to be enhanced so that fixing of the magnetization of the fixed magnetic layer is weakened, and as a result the direction of the magnetization is inclined with a discrepancy from the above-mentioned predetermined direction. This is associated with a problem that a waveform of the reproduction signal is distorted.
In order to weaken an influence of the demagnetizing field, there is known a spin valve element in which a fixed magnetic layer is constituted of a laminated ferrimagnetic film taking a three-layer structure of a first fixed magnetic layer indicative of ferromagnetism, a second fixed magnetic layer indicative of ferromagnetism and an opposite-parallel-coupling intermediate layer interposed between those first and second fixed magnetic layers, in which magnetizations of those fixed magnetic layers are coupled with each other in such a manner that those magnetizations are pointed in directions which are substantially parallel and mutually opposite. According to such a laminated ferrimagnetic film, the magnetizations of the first and second fixed magnetic layers come close to one another pointing in the opposite direction and running parallel. Thus, those magnetizations are kept being strongly fixed even if height in the element is reduced, so that a direction of the magnetization is stably maintained. In this manner, according to the SVMR head in which the laminated ferrimagnetic film is adopted in the fixed magnetic layer, it is possible to contribute to providing a higher output through reducing height in the element as mentioned above, while magnetization of the fixed magnetic layer is strongly fixed.
Further, there is known, other than the spin valve element in which the fixed magnetic layer is provided in form of the laminated ferrimagnetic film as mentioned above, a spin valve element in which a free magnetic layer is provided in form of a laminated ferrimagnetic film consisting of a first free magnetic layer, an opposite-parallel-coupling intermediate layer and a second free magnetic layer.
However, according to the SVMR head wherein the laminated ferrimagnetic layer is adopted for the free magnetic layer and the fixed magnetic layer, the laminated ferrimagnetic layer has, as mentioned above, two pieces of magnetization mutually pointed to the opposite directions, and a relative angle defined by a direction of magnetization of the free magnetic layer and a direction of magnetization of the fixed magnetic layer simultaneously takes two sorts of angle, for example, 0° and 180°. For this reason, magnetoresistive effects for the two sorts of angle are mixed. This is associated with such a defect that it is easy that the MR rate is lowered.
DISCLOSURE OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a magnetoresistive effect type of head that is high in the magnetoresistive rate (MR rate) while including the laminated ferrimagnetic film.
To achieve the above-mentioned object, the present invention provides a first magnetoresistive effect type of head having a magnetoresistive effect element offering a resistive change according to intensity of an external magnetic field, for detecting a magnitude of a resistance of the magnetoresistive effect element to detect intensity of a magnetic field,
Aoshima Ken-ichi
Kanai Hitoshi
Noma Kenji
Fujitsu Limited
Greer Burns & Crain Ltd.
Renner Craig A.
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