Bell Telephone Laboratories

At&t Bell Laboratories

Roy Conway Le Craw

Terence J Nelson

Lars C Luther

Raymond Wolfe

Ernst M Gyorgy

Stuart L Blank

Yttrium-iron magnetic domain materials having bismuth ions on dodecahedral sites are suitable for the manufacture of high-density, high-speed magnetic domain devices for operation at high and especially at very low temperatures. In these devices magnetic domain velocity is greater than 2000 centimeters per second per oersted, and magnetic domain diameter is less than 3 micrometers. A specified operational temperature range may extend from -150 to 150 degrees C.; accordingly, such devices are particularly suitable for operation aboard satellites, e.g., in satellite communications systems.

Magnetic domain device having a wide operational temperature range

The discovery of a magnetoresistive effect in oriented, crystalline, semiconducting iron garnet materials is used to design devices which detect the presence or orientation of magnetic fields. The principal measure of this effect is that the resistance between two electrodes (12) on the garnet body (11) varies as an imposed magnetic field (14, 15) produces a change in the direction of the magnetization of the body (11). This effect is useful when the garnet is so constituted as to possess a resistivity from 10.sup.3 to 10.sup.7 ohm-centimeters. Also, the anisotropy field of the garnet body must be comparable to less than the magnitude of the magnetic field to be detected. One aspect of particular utility for magnetic 'bubble' detectors (in magnetic bubble memories) is the isotropic character of the resistance when the magnetization is varied in the (111) plane but the significant change of resistance when the magnetization is moved to the [111] direction.

Garnet magnetoresistive sensor for magnetic fields

Members of a particular class of magnetic garnet compositions show characteristics useful for incorporation in magnetic memory devices which depend for their operation on the positioning of single wall domains ('bubbles'). Such compositions, ordinarily in the form of a supported layer, manifest high limiting bubble velocity, thereby making possible high record and access rates. Tetrahedral iron sites in the concerned compositions are occupied by non-magnetic ions in amount such as to result in magnetically balanced iron sub-lattices so that the magnetic moment contribution is made primarily by dodecahedral site ions. Europium is a necessary dodecahedral site occupant. High limiting velocity is attributed to the high value of the gyromagnetic ratio (g value) associated with europium.

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Summit, NJ, United States of America

Roy Conway Le Craw