Low-field magnetoresistance in La_(0.8)Sr_(0.2)Mn_3/ZrO_2 composite system

摘要

Nanosized La_(0.8)Sr_(0.2)MnO_3 (LSMO) are prepared by the sol-gel method. The ceramic composites (LSMO)_x/(ZrO_2)]_(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 percent and 8 percent 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.