Magnetism and transport properties of gamma-irradiated polymer-CrO2 composites

The transport properties of the gamma-irradiated CrO2-polymer composites were investigated. The resistance R is strongly current I dependent, except at high temperature where it displays a semiconductor-like temperature dependence for all currents. At low currents, I≤10 μA, as the temperature decreases far below the ferromagnetic transition, the resistance decreases first, then reaches a minimum, and at last increases again toward a second peak. At even lower temperatures, the second peak is followed by a metallic-like temperature dependence of R that ends at a cusp point marking the metal-insulator transition. The increase of the current shifts the cusp toward lower temperatures and the first minima toward higher temperatures. The resistance increases with the increase in current for all currents in the range 0.2≤I≤10 μA. For I≥50 μA, the resistance increases monotonically with the decrease in temperature in the whole temperature range but obeys different laws at low and high temperatures. An explanation attempt in terms of spin transport, disorder, and thermal effects is proposed.