Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
1999-06-14
2002-01-15
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S336000, C428S690000, C428S690000, C428S690000, C428S692100, C428S900000, C360S112000, C338S03200R, C324S252000
Reexamination Certificate
active
06338899
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetoresistance effect device, a magnetic head, a magnetic head assembly, and a magnetic recording/reproducing system. More precisely, it relates to a magnetoresistance effect device, a magnetic head, a magnetic head assembly, and a magnetic recording/reproducing system, in which is used a giant magnetoresistance effect element having high sensitivity and high reliability.
BACKGROUND OF THE INVENTION
The recent tendency in the art is toward small-sized, large-capacity magnetic recording media, for which there are increasing great expectations of high-power MR heads (magnetoresistance effect heads). For the MR film which is the basic constituent element in those MR heads, widely noticed is a spin valve film having a multi-layered magnetic film with a sandwich structure of magnetic layer
onmagnetic layer/magnetic layer, in which one magnetic layer is pinned for its magnetization owing to the magnetic coupling bias applied thereto (this layer may be referred to as a “pinned magnetic layer” or “pinned layer”) while the other magnetic layer is reversed for its magnetization owing to the applied magnetic field (this layer may be referred to as a “free magnetic layer” or “free layer”). The spin valve film of that type produces a giant magnetoresistance effect (GMR) through the relative angle change in the magnetization direction between those two magnetic layers.
As other types of MR films, known are an anisotropic magnetoresistance effect film (AMR film) made of an NiFe alloy or the like, an artificial lattice film, etc. Though smaller than that in an artificial lattice film, the MR ratio in a spin valve film is at least 4% and is much larger than that in an AMR film. A spin valve film can saturate its magnetization even in a low magnetic field, and is therefore suitable to MR heads. MR heads incorporating such a spin valve film receive much expectations for their practical applications. Specifically, for increasing the recording density in magnetic recording on magnetic discs and the like, high-sensitivity GMR heads (giant magnetoresistance effect heads) are indispensable.
Early GMR heads incorporate, in its GMR device, a spin valve film that comprises a free layer, a nonmagnetic spacer layer, a pinned magnetic layer and an antiferromagnetic layer. In those, the increase in the sensitivity of the film is indispensable for increasing the recording density through reduction in the recording track width. However, if the free layer is thinned so as to increase the sensitivity of the film for that purpose, the stray magnetic field from the pinned magnetic layer will shift the bias point. In that case, it is often difficult to effectively correct the thus-shifted operating point by the current magnetic field.
On the other hand, a so-called laminated pinned ferromagnetic layer (hereinafter referred to as “SyAF”, or “Synthetic AF”) has been proposed (U.S. Pat. No. 5,465,185), which comprises two ferromagnetic layers as antiferromagnetically coupled via an antiferromagnetically coupling layer existing therebetween. In principle, the antiferromagnetically coupled, pinned layer of that type would produce very small stray magnetic field, thereby readily ensuring the operating point.
One case of a spin valve film with SyAF is referred to, in which one of the two ferromagnetic layers adjacent to the nonmagnetic spacer layer is a ferromagnetic layer A while the other adjacent to the antiferromagnetic layer is a ferromagnetic layer B and in which the ferromagnetic layer A and the ferromagnetic layer B have the same magnetic thickness, thickness x saturation magnetization. In that case, the stray magnetic fields from the layer A and layer B cancel each other so that there is substantially no stray magnetic field generated by the pinned layer. As a result, the pinned layer of that type is no more susceptible to a magnetic field and has the significant advantage of stable pinned magnetization at around the blocking temperature, Tb, at which the magnetic coupling bias of the antiferromagnetic layer is lost.
SUMMARY OF THE INVENTION
The problem with the present technology, that an object of the present invention is to resolve, is that the inventors found, the bias point designing in an applied sense current is difficult, especially in device using thin free layer so as to increase the sensitivity of output signal for high density recording.
In a first aspect, the present invention provide a magnetoresistance effect element that attains the object mentioned above comprising a nonmagnetic spacer layer, a first ferromagnetic layer and a second ferromagnetic layer as separated by the nonmagnetic spacer layer, in which the first ferromagnetic layer has a magnetization direction different from the magnetization direction of the second ferromagnetic layer when the applied magnetic field is zero, and the second ferromagnetic layer comprises a pair of ferromagnetic films as antiferromagnetically coupled to each other and a coupling film that separates the pair of ferromagnetic films while antiferromagnetically coupling them, and a nonmagnetic high-conductivity layer adjacent to the first ferromagnetic layer on the plane opposite to the plane at which the first ferromagnetic layer is contacted with the nonmagnetic spacer layer.
In the present invention, the magnetoresistance effect device may realize extremely high sensitivity while maintaining a good bias point. Preferably, the MR device may be in the form of a so-called spin valve device (see U.S. Pat. No. 5,206,590), in which the first ferromagnetic layer is not coupled to the second ferromagnetic layer and the magnetization directions of the two layers are perpendicular to each other at zero applied magnetic field. Preferably, the applied magnetic field to change the magnetization of the first ferromagnetic layer may be smaller than that to change the magnetization of the second ferromagnetic layer, and the magnetization of the second ferromagnetic layer is pinned to such a degree that the magnetization direction may not change even in the presence of an applied magnetic field.
In the present invention, the nonmagnetic high-conductivity layer may contain an element of which the specific resistance in bulk at room temperature is not larger than 10 &mgr;&OHgr;cm, thereby realizing good characteristic, namely, high MR ratio owing to the spin filter effect in the ultra-thin first ferromagnetic layer and low Hcu.
For high density recording and for realizing the increase in MR ratio owing to the spin filter effect of the nonmagnetic high-conductivity layer, the thickness of the first ferromagnetic layer may be between 0.5 nanometers and 4.5 nanometers.
In the present invention, the thickness of the nonmagnetic high-conductivity layer and that of the second ferromagnetic layer may be so designed that the wave asymmetry, (V1−V2)/(V1+V2) , in which V1 indicates the peak value of the reproduction output in a positive signal field and V2 indicates the peak value of the reproduction output in a negative signal field, may fall between minus 0.1 and plus 0.1.
In the present invention, the MR device may satisfy the conditions of 0.5 nanometers≦tm(pin1)−tm(pin2)+t(HCL)≦4 nanometers and t(HCL)≧0.5 nanometers, in which t(HCL) indicates the thickness of the nonmagnetic high-conductivity layer (in terms of the Cu layer having a specific resistance of 10 &mgr;&OHgr;cm), and tm(pin1) and tm(pin2) indicate the magnetic thicknesses of the pair of ferromagnetic films, respectively, in the second ferromagnetic layer in terms of saturation magnetization of 1 Tesla, where pin 1 is of one of the ferromagnetic films disposed adjacent to the nonmagnetic spacer layer and pin2 is of another one of the ferromagnetic films. Satisfying the conditions noted above, the MR device may realize the wave asymmetry falling between minus 0.1 and plus 0.1 and high MR.
In the present invention, the first ferromagnetic layer may have a magnetic thickness, thickness×saturation magnetization, of smaller than 4
Fuke Hiromi
Fukuzawa Hideaki
Hashimoto Susumu
Iwasaki Hitoshi
Kamiguchi Yuzo
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