Low-field magnetoresistance in La0.8Sr0.2MnO3/ZrO2 composite system

Nanosized La0.8Sr0.2MnO3 (LSMO) are prepared by the sol-gel method. The ceramic composites (LSMO)x/(ZrO2)1−x are obtained using solid-state sintering. The magnetoresistance (MR) of composites is explored as a function of the manganite/insulator composition, temperature, and magnetic field. Enhancements of the low-field magnetoresistance (LFMR) are observed in the composites. For instance the MR ratios at 150 K with H = 300 Oe are 0.7% and 8% for the x = 0.8 and 0.25 samples, which are 4.5 times and 53 times as large as that for pure LSMO, respectively. The improved field sensitivity (dMR / dH) has a maximum at x = 0.25, around which the system exhibits a conduction percolation threshold. The spin-dependent tunneling and scattering at the interfaces of grain boundaries are responsible for the enhanced LFMR.