Number 179 (Story #3), May 17, 1994 by Phillip F. Schewe and Ben Stein A THOUSANDFOLD INCREASE IN THE MAGNETORESISTANCE (MR) in superlattice films has been observed by scientists at AT&T Bell Labs. The MR phenomenon, in which a material's electrical resistance is altered by a changing magnetic field, has already been used in magnetic recording heads. One figure of merit, the MR ratio, is the percentage change in resistance as an external magnetic field is switched between high and low values. The highest previous MR ratio was about 150% in a Fe-Cr multilayer film. The new MR ratio, obtained for 100 to 200-nm thick La-Ca-Mn-O films (grown epitaxially on a LaAlO3 substrate), is 127,000% at a temperature of 77 K and 1300% at room temperature. The field used was 6 Tesla. (S. Jin et al., Science, 15 April 1994.)