Japanese researchers have identified an oxide material that may soon greatly improve the storage capacity of hard disks and magnetic tapes. The discovery, reported in tomorrow's issue of Nature, relies on a phenomenon called colossal magnetoresistance--a large drop in a material's electrical resistance in response to an applied magnetic field--that has previously been seen only at very low temperatures.
Magnetoresistance is what allows the heads in a tape recorder or a disk drive to read data from the magnetic pattern on the tape or disk. It's the result of a particular magnetic property of materials--the magnetic moment, a tiny magnetic field produced by electrons orbiting the nucleus of an atom. In many crystalline materials, magnetic moments are randomly oriented, which increases the electrical resistance of the material. But a strong external magnetic field can reduce that resistance by bringing the magnetic moments into alignment. The larger the magnetoresistance of a material, the smaller the magnetic signal to which it can respond.
Until now, the largest resistance drops were seen only at very low temperatures; when using magnetoresistive materials in practical, everyday items, scientists had to settle for only a 1% or 2% reduction in resistance. But in crystals of an iron-molybdenum oxide, a team led by Kei-Ichiro Kobayashi at the Joint Research Center for Atom Technology in Tsukuba, Japan, saw a 10% drop in resistance when they placed the material in a strong magnetic field, considerably more than the one seen in comparable materials.
Because of the high magnetic field required to produce the magnetoresistance effect, Kobayashi says, the material isn't ready to be used in data storage devices. But scientists are heartened by the results. "[The change in resistance] is a huge effect," says Sang-Wook Cheong, a physicist at Rutgers University and Lucent Technologies' Bell Laboratories in New Jersey. The oxide's display of magnetoresistance at room temperature, he predicts, "will lead to more research on [similar] materials." And, Cheong adds, the possibility of turning this finding into improved disk storage and magnetic sensors "is very realistic."