Magnetic and magnetoresistance properties in (La0.67Ca0.33MnO3)/(ZrO2)1-x composite system

(La0.67Ca0.33MnO3)(x)/(ZrO2)(1-x) is the volume fraction ratio) percolated composites were fabricated by combining La0.67Ca0.33MnO3 (LCMO) powders with ZrO2 particles, where LCMO powders were prepared by sol-gel process. Low field magnetoresistance (LFMR) is greatly enhanced at low temperature when the system is close to the metallic percolation threshold of x = 0.4. The magnetoresistance ratio of (LCMO)(0.4)(ZrO2)(0.6) in a 10 mT magnetic field at 77 K is 7.8%, about 7.12 times larger than that of pure LCMO compound. The enhancement of spin-dependent tunneling of electrons at the interfaces between LCMO and ZrO2 grains is responsible for the enhanced LFMR. With increasing ZrO2 addition, Curie temperature T-C decreases firstly and then remains constant at about 220 K when x < 60%, showing limited substitution effect of Zr ions on B sites.