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Date: Mon, 29 Jul 96 10:18:54 EDT From: physnews@aip.org (AIP listserver) Subject: update.281
PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 281 July 29, 1996 by Phillip F. Schewe and Ben Stein
SOLAR NEUTRINO FLUX IS NOT CORRELATED WITH SUNSPOT ACTIVITY. The Kamiokande detector, situated a
THE PHYSICS OLYMPIAD IN OSLO, like the sports Olympiad
TUNNEL JUNCTION MAGNETORESISTANCE may lead to higher-density magnetic storage devices. Physicists have known for some time that sandwiches of alternating magnetic and nonmagnetic microlayers can undergo a change in electrical resistance in the presence of an external magnetic field (arising, say, from a tiny domain on a segment of magnetic tape). This magnetoresistance (MR) effect can be used to decode binary data and has been employed in reading heads in computer hard drives. Giant magnetoresistance (GMR), a stronger version of MR, affords even greater data-decoding sensitivity. Prototype hard-drives with read heads using GMR have achieved areal data densities of 3 Gbits/sq.in. Tunnel junction magnetoresistance (JMR) is yet another approach to transforming a tiny magnetic field into a change in resistance. Unlike the all-metal GMR sensor, a room-temperature JMR sensor consists of two metal (ferromagnetic) layers separated by an insulating layer. A JMR trilayer junction tested recently at MIT is only 20 nm thick and the signal (the fractional change in resistance) was 23%, compared to a signal of less than 7% for a 40-nm-thick, 4-layer GMR prototype. MIT physicist Jagadeesh Moodera (moodera@slipknot.mit.edu; 617-253-5423) suggests that the more compact size, relatively larger signal, and the low sub-nanoamp operating current of the JMR sensor could make for easier engineering of devices and lower production costs. An areal density of more than 10 Gbits/sq.in. is possible, he says. (J.S. Moodera et al., Applied Physics Letters, 29 July.)