Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-05-17
2002-03-26
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S403000, C428S404000, C428S900000, C360S112000, C324S252000, C252S06251C, C427S127000, C427S128000, C427S129000, C427S130000
Reexamination Certificate
active
06361863
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates to devices having magnetoresistive material and, more particularly to devices having magnetoresistive material comprising two-phase metallic ferromagnetic components which exhibit the giant magnetoresistance (GMR) effect.
A typical measure of magnetoresistance is given by
&Dgr;&rgr;/&rgr;=(&rgr;
0
−&rgr;
H sat
)/&rgr;
Hsat
,
where &rgr;
Hsat
is the resistivity of the material when the applied magnetic field is at the saturation value H
sat
and &rgr;
0
is the resistivity of the material when the applied magnetic field is 0. The GMR effect, where the magnetoresistance ratio, &Dgr;&rgr;/&rgr;, is greater than a fraction of a percent, was first discovered in multilayered thin film structures and subsequently in metallic films containing magnetic particles (magnetic granular films). More recently, large &Dgr;&rgr;/&rgr; has been observed in a device called a magnetic tunnel junction (MTJ), in which two ferromagnetic electrodes are separated by an insulating layer that is thin enough to permit quantum mechanical tunneling between the two electrodes. The tunneling phenomenon is electron-spin dependent, making the magnetic response of the MTJ a function of the relative orientations of the spin polarizations of the two electrodes. Although thin film GMR and MTJ devices are useful for sensing magnetic field and other applications involving small scales, such as sensing magnetically stored information in a computer disk memory, they are not suited to large scale applications such as in anti-lock braking systems for vehicles and rotary machine feedback systems, which require bulk quantities, sheets or thick films of magnetoresistive material. Moreover, such large scale applications typically require the device to operate at normal ambient temperatures, such as room temperature (300° K).
U.S. Pat. No. 5,856,008 to Cheong et al. describes forming a magnetoresistive material consisting of compacted CrO
2
powder with the grains of the powder at least partially coated with a thin layer of insulating Cr
2
O
3
. Although the Cheong et al. patent describes this material as having a magnetoresistance ratio of greater than 12%, such a high magnetoresistance ratio was achieved only at a cryogenic temperature of 5° K and a relatively high magnetic field of 20,000 Oe. The data contained in the Cheong et al. patent shows that the material has a magnetoresistance ratio of 0.2% at 200° K and 1000 Oe, and there is no data in the patent showing that the material has any GMR effect at normal ambient temperatures, such as room temperature (300° K).
The Cheong et al. patent provides an explanation for the desirable magnetoresistance ratio as being attributable to spin-polarlized tunneling between grains, with the insulating material, i.e., Cr
3
O
2
, enhancing the spin-polarization effect, and cites the references J. Inoue et al., “Theory of Tunneling Magnetoresistance in Granular Magnetic Films,” Physical Review B., Vol. 53, No. 16, at 927, and Miyazaki et al., “Spin Polarized Tunneling in Ferro Magnet/Insulator/Ferro Magnet Junctions,” Journal of Magnetism and Magnetic Materials,” 151, at 403 in support of the explanation. However, the GMR effect in the Cheong et al. material can only be obtained at cryogenic temperatures which makes it unsuitable for the large scaled applications, such as the ones mentioned above.
Accordingly, what is needed is a GMR material which can be made in bulk and which exhibits a high magnetoresistance ratio at normal ambient temperatures, e.g., room temperature.
SUMMARY OF THE INVENTION
The invention provides a device comprising a magnetoresistive material that includes a first metallic ferromagnetic powder material at least partially coated with a thin insulating material and a second metallic ferromagnetic material in contact with the granules of the first metallic ferromagnetic powder material, the granules of the first ferromagnetic powder material having a higher coercive field than the second ferromagnetic material. According to an exemplary embodiment of the present invention, the granules of the first metallic ferromagnetic material are relatively hard, and the second metallic ferromagnetic material is also in powder form having granules which are relatively soft, the first and second metallic ferromagnetic powder materials being mixed and compressed to form a compacted mixture. According to a still further exemplary embodiment of the present invention, the first metallic ferromagnetic powder material has CrO
2
granules at least partially coated with a thin layer of Cr
2
O
3
, and the second metallic ferromagnetic powder material has Ni granules.
Another aspect of the present invention is a method for making a device comprising a magnetoresistive material including the steps of mixing a first metallic ferromagnetic powder material having relatively hard granules at least partially coated with a thin insulating material, and a second metallic ferromagnetic powder material having relatively soft granules, the granules of the first ferromagnetic powder material having a higher coercive field than the granules of the second ferromagnetic powder material, and compressing, rolling or extruding the mixture to form a compacted magnetoresistive material. The magnetoresistive material in the device of the invention typically exhibits a magnetoresistance ratio of 8% at room temperature (i.e., 300° K) in a magnetic field of about 4000 Oe applied substantially perpendicular to the direction of current flow in the material and a magnetoresistance ratio of 12% under the same conditions except that the direction of the applied magnetic field is parallel to the direction of current flow in the material.
REFERENCES:
patent: 5856008 (1999-01-01), Cheong
Xiao, et al. “Giant Magnetoresistance. . . ” Physical Review Letters Jun. 22, 1992.*
Inoue et al. “Theory of tunneling . . . ” Physical Review B May 1, 1996.*
Inoue et al., “Theory of tunneling magnetoresistance in granular magnetic films,”Physical Review B, vol. 53, No. 18, pp. R11 927-R11 929 (May 1, 1996).
Miyazaki et al., “Spin polarized in ferromagnet/insulator/ferromagnet junctions,”Journal of Magnetism and Magnetic Materials, vol. 151, pp. 403-410 (1995).
Daughton et al., “Magnetic Field Sensors Using GMR Multilayer,”IEEE Transactions on Magnetics, vol. 30, No. 6, pp. 4608-4610 (Nov., 1994).
Hylton et al., “Giant Magnetoresistance at Low Fields in Discontinuous NiFe-Ag Multilayer Thin Films”,Science, vol. 261, pp. 1021-1024 (Aug., 1993).
Ranmuthu et al., “New Low Current Memory Modes with Giant Magneto-Resistance Materials,”IEEE Transactions on Magnetics, vol. 29, No. 6 (Nov., 1993).
Zhang, “Theory of giant magnetoresistance in magnetic granular films,”Appl. Phys. Lett., vol. 61, No. 15, pp. 1855-1857 (Oct., 1992).
Berkowitz et al., “Giant Magnetoresistance in Heterogeneous Cu-Co Alloys,”Physical Review Letters, vol. 68, No. 25, pp. 3745-3748 (Jun., 1992).
Xiao et al., “Giant Magnetoresistance in Nonmultilayer Magnetic Systems”,Physical Review Letters, vol. 68, No. 25, pp. 3749-3752 (Jun., 1992).
Parkin, “Oscillations in giant magnetoresistance and antiferromagnetic coupling in [Ni81Fe19/Cu]Nmultilayers,”Appl. Phys. Lett. vol. 60, No. 4, pp. 512-514 (Jan., 1992).
Daughton et al., “Giant Magnetoresistance in Narrow Stripes”,IEEE Transactions on Magnetics, vol. 28, No. 5, pp. 2488-2493 (Sep., 1992).
Nakatani et al. “Giant Magnetoresistance in Ni-Fe/Cu Multilayers Formed by Ion Beam Sputtering,”IEEE Transactions on Magnetics, vol. 28, No. 5, pp. 2668-2670 (Sep., 1992).
White, “Giant Magnetoresistance: A Primer,”IEEE Transactions on Magnetics, vol. 28, No. 5, pp. 2482-2487 (Sep., 1992).
Pratt et al., “Perpendicular Giant Magnetoresistances of Ag/Co Multilayers,”Physical Review Letters, vol. 66, No. 23, pp. 3060-3063 (Jun., 1991).
Dieny et al., “Giant magnetoresistance in soft ferromagnetic multilayers”,Physical Review B, vol. 43, No. 1, pp. 1297-1300 (Jan., 1991).
Mosca et al., “Oscillatory interlayer coupling and giant magnetoresistance in Co/Cu multilay
Gambino Richard J.
Shin Dong-il
Baker & Botts LLP
Kiliman Leszek
The Research Foundation of State University of New York
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