1. The James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA
2. Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
3. Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey 07974, USA

Correspondence to: T. F. Rosenbaum¹ Correspondence and requests for materials should be addressed to T.F.R. (e-mail: Email: t-rosenbaum@uchicago.edu).

Abstract

Several materials have been identified over the past few years as promising candidates for the development of new generations of magnetoresistive devices. These range from artificially engineered magnetic multilayers¹ and granular alloys²,³, in which the magnetic-field response of interfacial spins modulates electron transport to give rise to 'giant' magnetoresistance⁴, to the manganite perovskites^{5, 6, 7}, in which metal–insulator transitions driven by a magnetic field give rise to a 'colossal' magnetoresistive response (albeit at very high fields). Here we describe a hitherto unexplored class of magnetoresistive compounds, the silver chalcogenides. At high temperatures, the compounds Ag₂S, Ag₂Se and Ag₂Te are superionic conductors; below 400 K, ion migration is effectively frozen and the compounds are non-magnetic semiconductors⁸,⁹ that exhibit no appreciable magnetoresistance¹⁰. We show that slightly altering the stoichiometry can lead to a marked increase in the magnetic response. At room temperature and in a magnetic field of 55 kOe, Ag₂₊Se and Ag₂₊Te show resistance increases of up to 200%, which are comparable with the colossal-magnetoresistance materials. Moreover, the resistance of our most responsive samples exhibits an unusual linear dependence on magnetic field, indicating both a potentially useful response down to fields of practical importance and a peculiarly long length scale associated with the underlying mechanism.