Magnetoresistance in microwave synthesizedAg2+δSe(0.0<~δ<~0.2)

Abstract

Compositional variation of magnetoresistance (MR) ratio with silver excess stoichiometry in ${\mathrm{Ag}}_{2+\ensuremath{\delta}}\mathrm{Se}$ samples has been studied employing a synthetic approach to prepare instantly a series of bulk silver selenide compounds using microwave energy. Bulk density g99% is achieved in situ, by means of volumetric heating/sintering in less than 10 min, which makes this process unique compared to other chemical and nonchemical approaches. We observe a systematic decrease in metal-insulator transition with increasing Ag. Magnetoresistance ratio observed in transverse geometry is 145%, greater than the longitudinal geometry (70%). This series shows linear dependence of MR with higher fields $(3lHl16\mathrm{T})$ with no saturation of MR ratio even at 16 T in transverse mode. However, a distinct saturation effect was noticed in almost all the compositions for magnetic field above 13 T in longitudinal mode. Electron probe microanalysis shows an elemental-rich selenium phase for $\ensuremath{\delta}=0.05$ composition which accounts for low resistivity, large magnetoresistance ratio and unsymmetrical MR curves when field is applied in both the directions. This is attributed to the charge density fluctuations in chemically inhomogeneous systems. At 300 K, MR ratios of 30 and 59 % for $\ensuremath{\delta}=0.2,$ in longitudinal and transverse mode is observed, respectively.