IBM Corp’s AdStar unit duly unveiled its possible sidk storage breakthrough (CI No 2,236), saying it has discovered a new method of producing the phenomenon called giant magnetoresistance, and suggesting that it might find its way into storage products by the end of the decade, leading to storage density of up to 10G-bits per square inch of surface area, about 30 times the present limit of 350M-bits per square inch. The secret is a practical new way to generate a large increase in the electrical resistance of a multi-layered metal as it moves near a tiny spot of magnetic material so that future heads can detect weak magnetic fields produced by very small magnetised spots, and the concept is an extension of the magnetoresistive head technology used in today’s drives introduced by IBM in 1991. IBM says that densities using magnetoresistive heads is doubling every 18 months, compared with 30% a year with inductive film heads. Magnetoresistive materials change their resistance in the presence of a magnetic field and the giant magnetoresistive effect produced an electrical signal more than five times as strong as that produced by conventional magnetoresistive heads, so that it should be able to detect much weaker magnetism. The sensors were fabricated as stacks of thin layers of alternating magnetic nickel-iron alloy and non-magnetic silver, all laid down by sputtering.
