To makers of computer disk drives, the fainter the magnetic field a sensor can detect, the better. If data-reading heads can detect tinier data bits, which have weaker fields, manufacturers can cram more data into less disk space (SN: 4/3/99, p. 223).
Today, commercial read heads are made of layers of magnetic metals stacked into sandwich structures whose electrical resistance changes in response to a varying magnetic field. These so-called giant magnetoresistance heads change their resistance at room temperature by about 5 percent in the presence of a magnetic bit of data, says Stuart A. Solin of NEC Research Institute in Princeton, N.J.
Science News headlines, in your inbox
Headlines and summaries of the latest Science News articles, delivered to your email inbox every Thursday.
Thank you for signing up!
There was a problem signing you up.
In the Sept. 1 Science, he and his colleagues unveil a new type of magnetoresistive device about the size of a pinhead. More like a traffic rotary for electrons than a sandwich, it could raise commercially useful magnetoresistance to new heights.
In more recent, unpublished experiments, “we’ve already obtained over 2,000 percent [resistance change] at magnetic fields relevant to read heads,” Solin told Science News. At high magnetic fields, the researchers have measured resistance change of up to 1 million percent.
Solin and his colleagues have coined a new phrase to describe their invention’s behavior: “extraordinary magnetoresistance.” To make a device demonstrating the effect, the researchers first deposit a ring of indium-antimonide, about a micrometer thick, onto a gallium-arsenide plate. Then, they fill its center with gold.
In the absence of a magnetic field, current passes handily through the gold, so the resistance is tiny. However, a magnetic field exerts a perpendicular force on moving electrons. As the researchers raise the magnetic field, this deflection forces more current into the indium-antimonide, where resistance is high.