Large magnetoresistance in non-magnetic silver chalcogenides

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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 perovskites5,6,7, 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+δSe and Ag2+δTe 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.

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Figure 1: Resistivity ρ as a function of temperature T at a series of magnetic fields H = 0, 9, 17, 26,36, 48 and 55 kOe for Ag2+δSe (a) and H = 0, 10, 20, 29, 35, 43 and 55 kOe for Ag2+δTe (b).
Figure 2: The normalized magnetoresistance Δρ(T, H )/ρ(T, 0) for Ag2+δSe as a function of magnetic field H at a series of temperatures T = 4.5, 30, 60, 90, 180, 270 and 300 K.
Figure 3: Comparison of the normalized magnetoresistance of the silver chalcogenides and a representative colossal-magnetoresistance material at H = 40 kOe.
Figure 4: Hall coefficient R H (n-type) plotted against T −1for a set of silver chalcogenide samples labelled by their magnetoresistive response (at T = 4.5 K and H = 55 kOe).

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Acknowledgements

We thank D. L. Price and B. J. Wuensch for discussions. The work at the University of Chicago was supported primarily by the MRSEC Program of the National Science Foundation. The work at Argonne National Laboratory was supported by DOE Basic Energy Sciences.

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Correspondence to T. F. Rosenbaum.

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