Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-09-25
2004-03-23
Heinz, A. J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06710984
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetoresistance effect element detecting the change of an external magnetic field, a magnetoresistance effect head equipped with the magnetoresistance effect element, a magnetic reproducing apparatus mounting the magnetoresistance effect head, and further a magnetic laminate having two ferromagnetic layers the magnetization directions of which cross approximately perpendicularly.
BACKGROUND OF THE INVENTION
Hitherto, for reading magnetic information recorded in a magnetic recording medium, a method of relatively moving a reproducing magnetic head having a coil and a recording medium and detecting the voltage induced to the coil by the magnetic induction generated at the case has been used. Thereafter, a magnetoresistance effect element (hereinafter, referred to as an MR element) reproducing magnetic information by utilizing a magnetoresistance effect that the electric resistance of a specific ferromagnetic substance changes in response to the intensity of an external magnetic field was developed (see, IEEE MAG-7, 150 (1971), etc.). The MR element is used for a magnetic field sensor as well as is used as a magnetoresistance effect head (hereinafter, referred to as MR head) mounted on a magnetic reproducing apparatus such as a hard disk drive, etc.
Recent efforts have been made to obtain small size and increased capacity in a magnetic recording medium mounted on a magnetic reproducing apparatus. However, the relative speed of a magnetic head for reproducing and a magnetic recording medium at information reading becomes slower, and the expectation to obtain an MR head capable of obtaining a large output even with a slow relative speed has been increased.
For such an expectation, a very large magnetoresistance effect film has been developed. The very large magnetoresistance effect film is a multilayer film, or so-called artificial lattice film formed by alternately laminating ferromagnetic metal films and non-magnetic metal films, such as Fe/Cr and Fe/Cu, and antiferromagnetically-coupling the adjacent ferromagnetic metal films [see, Phys. Rev. Lett., 61, 2474(1988); Phys. Rev. Lett., 64, 2304(1990), etc.]. However, because in the artificial lattice film, the magnetic field required for saturating the magnetization is large, the artificial lattice film is not suitable as a film material for the MR head.
On the other hand, there is reported an example that a large magnetoresistance effect is realized in the MR film of a multilayer film composed of a ferromagnetic metal layer/a non-magnetic metal layer/a ferromagnetic metal layer formed by holding the non-magnetic metal layer between the upper and lower ferromagnetic metal layers, wherein the two ferromagnetic metal layers are not magnetically-coupled (non-coupling). The MR film has the feature that the magnetization (spin) of one ferromagnetic metal layer is fixed and the magnetization of the other ferromagnetic metal layer is magnetization-inverted by an external magnetic field. Thereby, by changing the relative angles to the spin directions of the ferromagnetic metal layers disposed holding a non-magnetic layer between them, a magnetoresistance effect is obtained, whereby such an MR element is called a spin valve element (see, Phys. Rev. B 45, 806(1992); J. Appl. Phys. 69, 4774(1991), etc.).
Although the rate of change of the magnetoresistance of such a spin valve element is small as compared with the artificial lattice film, because the magnetic field required for saturating the magnetization is small, the element is suitable for the use of MR head, and the element has already been practically used.
A general spin valve element has a laminated structure of a ferromagnetic free layer, an intermediate non-magnetic layer, a ferromagnetic pin layer, and an antiferromagnetic layer. The magnetization of the ferromagnetic pin layer adjacent to the antiferromagnetic layer is fixed to one direction under an external magnetic field by an exchange bias magnetic field from the antiferromagnetic layer. On the other hand, the ferromagnetic free layer can be freely rotated to an external magnetic field and the parallel/anti-parallel state of the magnetizations of the ferromagnetic free layer and the ferromagnetic pin layer can be easily realized in a low magnetic field. In addition, when the magnetizations of both the ferromagnetic layers are in a parallel state, the electric resistance of the element is low, and when the magnetizations are in an anti-parallel state, the electric resistance becomes high. In the spin valve element, by increasing the difference of the two resistance values, high magnetoresistance effect amplitude is obtained.
When the spin valve element is practically used, to obtain a high susceptibility by utilizing the linear region of the resistant change, it is preferred to apply a bias such that the magnetization of the ferromagnetic free layer crosses the magnetization of the pin layer at about a right angle in a zero magnetic field. The bias is also important in the meaning that the magnetization of the free layer becomes a simple magnetic domain so that Barkhausen noise is not generated in the case of rotating the magnetization of the free layer to an external magnetic field. A hard magnetic film having the same function as a magnet is formed at the side surface of the spin valve film for forming a single magnetic domain in the magnetic layer.
When the thickness of the hard magnetic film is same as the thickness of the ferromagnetic free layer, a proper bias can be applied and when the thickness of the hard magnetic layer is thinner than the above-described thickness, the formation of the simple magnetic domain of the ferromagnetic free layer is hard to attain due to an insufficient bias. Also, when the thickness of the hard magnetic film becomes thicker than the thickness of the free layer, the bias becomes excessive, whereby the permeability of the ferromagnetic free layer is lowered.
However, under present conditions, when the thickness of the hard magnetic film is thinned to a thickness the same as that of the ferromagnetic free layer, because the joining area of both the members becomes small, magnetic joining cannot be made well, and thus, the hard magnetic film must be made thicker than the thickness of the ferromagnetic free layer. As the result thereof, a bias applied to the ferromagnetic free layer becomes excessive, whereby the permeability of the ferromagnetic free layer is lowered to give a loss to the susceptibility and the output.
For solving these problems, a spin valve element employing the construction that an antiferromagnetic layer of a definite form is laminated to the end portion of the free layer to fix the magnetization of the end portion of the free layer by the exchange coupling of the antiferromagnetic layer and the free layer, and a bias is applied from the portion to the central magnetic field response portion of the free layer is proposed. Because the construction is a bias method using the antiferromagnetic layer worked in a definite form (pattern), the construction is called a patterned bias structure.
A slant view of a spin valve element of the patterned bias structure is shown in FIG.
1
A. The spin valve element has a first antiferromagnetic layer
1
, a ferromagnetic pin layer
3
, an intermediate non-magnetic layer
5
, and a ferromagnetic free layer
7
successively laminated from below, and further has a pair of second antiferromagnetic layers
9
laminated to both ends of the ferromagnetic free layer
7
in the lengthwise direction and a pair of lead electrodes
11
. Both ends of the ferromagnetic free layer
7
and the ferromagnetic pin layer
3
are applied with the magnetization of uni-directional anisotropy in
FIG. 1A
by the magnetic exchange coupling of each of the second antiferromagnetic layers
9
and the first antiferromagnetic layer
1
. That is, both end portions (oblique line portions) of the ferromagnetic free layer
7
laminated with the second antiferromagnetic layers
9
are magnetization fixe
Kamiguchi Yuzo
Yuasa Hiromi
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