International Business Machines Corporation

Erik Klokholm

Joseph Adam Aboaf

Thomas S Plaskett

Thomas R McGuire

Sigrid R Herd

Devices and circuits are described employing magnetoresistive materials exhibiting a negative .DELTA..rho. effect (.DELTA..rho.=.rho..parallel.-.rho..perp.). In these materials, the electrical resistivity .rho. of the material in a direction perpendicular to the direction of current through the material is greater than the electrical resistivity .rho..parallel. of the material in a direction parallel to the direction of the electrical current through the material. These are ferromagnetic materials exhibiting magnetoresistance in the presence of an electrical current through the material and a magnetic field applied to the material to magnetize it to saturation at room temperature. These devices and circuits have advantages over conventional devices and circuits employing magnetoresistive materials of the conventional type, in which .DELTA..rho. is a positive quantity.

New magnetoresistive materials

An alloy of Co.sub.x Pt.sub.y with y between 10 and 30 at. % is made by sputtering with H.sub.c &gt;500 Oe and 4.pi.M.sub.s &gt;5000 gauss, and zero magnetostriction. For 10 to 30 at. % Co the sputtered alloy has an H.sub.c of 500-1000 Oe with 4.pi.M.sub.s of 4000-14000 gauss, a magnetostriction passing through zero between 20 and 30 at. % of Pt. For thickness below 1000.ANG. H.sub.c is large (for the above range of alloys) and magnetization is also larger and coercivity varies as a direct function of Pt composition in the alloy up to 30 at. %.

Zero to low magnetostriction, high coercivity, polycrystalline, Co-Pt

A low or zero magnetostriction ferromagnetic alloy is used for a magnetic recording medium. The alloy is (Fe.sub.y Co.sub.1-y).sub.1-x Cr.sub.x where y (Fe) is preferably 15-23 atomic percent of the FeCo part of the alloy. The value of x (Cr) is 7-20 atomic percent of the alloy and the remainder 1-x (FeCo) is 83-92 atomic percent of the alloy. The maximum ranges of the composition of the alloy are about as follows:

Zero magnetostriction Fe-Co-Cr magnetic recording media

An amorphous alloy of cobalt and from about 14 to 30 atomic percent of titanium can be deposited upon a substrate by r.f. sputtering from 10 to 30 percent of titanium. The properties of the amrophous CoTi films are similar to those of transition metal-metalloid glasses in that they have soft magnetic properties (low H.sub.c) and their resistivity is in the 100-200 micro-ohm centimeter range. Unlike most metal-metalloid glasses, these films have very low magnetostriction and they are more stable to thermal annealing. They are more corrosion resistant than permalloy plated films. The films can be employed as magnetic yoke layers in magnetic recording heads or in the bubble propagation structures of bubble domain devices, as substitutes for 80:20 Ni:Fe alloys. The FeCoTi, NiCoTi and FeNiCoTi amorphous alloys have similar characteristics to the CoTi amorphous alloys for Ti concentrations on the order of 14 to 30 atomic percent where the ratio of Co to Fe and or Ni is greater than or equal to about 1 to 1.

Amorphous Co-Ti alloys

Bubble domain devices using conventionally known elements for providing a plurality of bubble domain functions, including writing, storage and reading, are provided using a magnetic medium of garnet structure characterized by the presence of a single rare earth ion present in all available dodecahedral lattice sites. These devices operate well over room temperature ranges. This material has sufficiently high anisotropy (of the order 10.sup.5 ergs/cm.sup.3) to support stable magnetic bubble domains in the material. The anisotropy is growth induced and cannot be explained by conventionally accepted theories of anisotropy in garnet bubble domain materials. In preferred embodiments, these rare earth iron garnet films are deposited on suitable substances, which can be any non-magnetic materials having suitable lattice constants to provide substantial lattice match with the magnetic garnet films. Examples are Eu.sub.3 Fe.sub.5 O.sub.12 on Nd.sub.3 Ga.sub.5 O.sub.12 or (Pr,Sm).sub.3 Ga.sub.5 O.sub.12 substrates; and Sm.sub.3 Fe.sub.5 O.sub.12 on (Pr,Nd).sub.3 Ga.sub.5 O.sub.12 substrates.

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Stamford, CT, United States of America

Erik Klokholm