Magnetic and magnetotransport properties of half-metallic CrO2-SnO2 composites

Half-metallic (CrO2)(1-x)-(SnO2)(x) composites were prepared under high temperature and high pressure conditions. The composites are composed of large rod-like CrO2 grains and small SnO2 nanoparticles. The CrO2 in the composites is very pure and its saturation magnetization is very close to the theoretical value. The composition dependence of magnetic and magnetotransport properties of the composites was studied. The coercive force (H-c) and remanence ratio (M-r/M-s) of the composites increase dramatically with increasing SnO2 content x for x > 0.6. This should be due to that the CrO2 grains have been well separated by SnO2 nanoparticles and the magnetic interactions among CrO2 grains become weak when x > 0.6. The resistivity and magnetoresistance at 5 K of the composites increase with increasing x, and the increase quickens up at x = 0.5. When x >= 0.5, the (CrO2)(1-x)-(SnO2)(x) composites show insulator behavior, and the temperature dependence of the resistivity can be well described by fluctuation-induced tunneling model. But when x <= 0.4, the (CrO2)(1-x)-(SnO2)(x) composites show insulator-metal transitions, and the transition temperature increases with increasing SnO2 concentration. Below the transition temperature, their resistivity can also be explained by fluctuation-induced tunneling model. The (CrO2)(1-x)-(SnO2)(x) composites show greater magnetoresistance than pure CrO2 at low temperature, which is attributed to enhancement of tunneling magnetoresistance by adding of SnO2. (C) 2013 AIP Publishing LLC.