Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-10-18
2003-05-13
Ometz, David L. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06563679
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to giant magnetoresistance (“GMR”) transducers or read heads for reading magnetic signals from magnetic recording media, and more particularly, to current perpendicular-to-the-plane giant magnetoresistance (“CPP-GMR”) designs. While the invention finds particular application in conjunction with reading hard disk drives, the invention can be implemented with other magnetic storage media. Moreover, the invention can be implemented in other magnetic field detection devices as well as in other devices and environments.
2. Description of the Related Art
Giant magnetoresistance (GMR) was initially described by Baibich et al. in Physical Review Letters, Volume 61, No. 21, pp. 2472-2475 (1988), which is hereby incorporated by reference. GMR occurs when an application of an external field causes a variation in the relative orientation of the magnetizations of neighboring ferromagnetic layers. This in turn causes a change in the spin-dependent scattering of conduction electrons, thereby changing the electrical resistance of the structure. The discovery of GMR triggered a wide study of transport properties of magnetic multilayers. In most cases, the current flows-in-the plane of the layers, called CIP-MR.
Pratt et al. extended the GMR measurements to the case where the current flows perpendicular-to-the-plane, called CPP-MR as described in Pratt et al., Physical Review Letters, Volume 66, pp. 3060 (1991), which is hereby incorporated by reference. In general, the CPP-MR effect is several times larger than the CIP-MR effect. For MR read head applications, the CPP-MR element has to be dramatically scaled down (<100 nm) because of the very small specific resistance of the MR element with the CPP configuration.
In both CIP-MR and CPP-MR, the application of an external field causes a variation in the relative orientation of the magnetizations of neighboring ferromagnetic layers. This in turn causes a change in the spin-dependent scattering of conduction electrons and thus the electrical resistance of the structure. Theoretically, the resistance for CPP multilayers with a unique type of magnetic layer varies approximately as R(&thgr;)/R
ap
=1−a·cos
2
(&thgr;/2), where R(&thgr;) is the resistance in an external field, R
ap
(ap refers to antiparallel) is the resistance at zero field, &thgr; is the angle between the magnetization of successive or neighboring magnetic layers, and 0<a<1. Dauguet et al., Physical Review B, Volume 54, pp. 1083-87 (July 1996). Thus, the resistance versus magnetic field for a CPP multilayer is a typical parabolic curve. As a result, in order to apply CPP-MR for MR heads, a transverse magnetic bias to the CPP multilayer is required.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a CPP-MR read head with novel transverse magnetic bias that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a CPP-MR head includes a top shield and a bottom shield formed of magnetically shielding, electrically-conductive material. A multilayer magnetoresistance (MR) structure is disposed between the top shield and the bottom shield. The MR structure is in electrical contact with the top and bottom shields. A transverse magnetic field generating structure is adjacent the MR structure to transversely, magnetically bias the MR structure.
In another aspect of the present invention, a method of magnetically biasing a CPP-GMR read head is provided. The read head includes a multilayer GMR structure comprising a bilayer portion represented by [F/NM]
n
, where F represents a ferromagnetic material, NM represents a non-magnetic material, and n is an integer greater than or equal to 2 referring to the number of times the bilayer is repeated. The GMR structure is transversely magnetically biased using at least one magnet. Magnetic flux of the magnet is directed through the GMR structure using a soft magnetic layer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
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Baibich et al., “Giant Magnetoresistance of (001) Fe/(001)Cr Magnetic Superlattices”, Physical Review Letters, 1988 The American Physical Society, vol. 61, No. 21, pp. 2472-2475 (Nov. 21, 1988).
Dauguet et al., “Angular Dependence of the Perpendicular Giant Magnetoresistance of Multilayers”, 1996 The American Physical Society, vol. 54, No. 2, pp. 1083-1087 (Jul. 1, 1996-II).
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Araki Satoru
Li Shuxiang
Ometz David L.
TDK Corporation
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