Number 84 (Story #2), June 15, 1992 by Phillip F. Schewe and Ben Stein MAGNETORESISTANCE is a process, widely employed in the recording industry, in which magnetic fields are used to change the resistance of a conducting medium. In certain "magnetic superlattices," stacked materials in which thin layers of magnetic atoms (e.g., iron) and non-magnetic atoms (e.g., chromium) alternate, an even larger, "giant," magnetoresistance (GMR) effect can be produced, as of four years ago, although theorists largely cannot explain how it happens. Now two research teams have observed GMR effects in non-layered materials, a development which may make the materials easier to use in magnetic recording heads. In one experiment, for example, a UCSD-LBL-NYU collaboration studied thin films containing cobalt-rich particles in a copper-rich matrix. (J.Q. Xiao et al. and A.E. Berkowitz et al., Phys. Rev. Lett., 22 June.)