Resistivity and magnetotransport in CrO₂ films

The resistivity of films of the metallic magnet CrO₂ deposited onto ZrO₂ substrates has been measured in the temperature range T=1.6 to 410 K. Longitudinal and transverse magnetoresistances have also been measured between 0.55 and 380 K in magnetic fields up to 10 T. The resistivity has a decrease in slope as a function of temperature at the Curie point, T_c=390K, and becomes linear in temperature below about 5 K. The magnetoresistances (MR) for both field orientations are negative and linear with field above about 200 K for fields up to 3 T, while they show a concave dependence on field below that temperature. Their magnitude decreases with decreasing temperature down to 200 K and then increases for temperatures down to 5 K. Below 5 K, the longitudinal MR values decrease and the transverse values stay about constant as T is lowered. Below 100 K, the resistance in a transverse field has a minimum at about 3 T. Chromium dioxide has been found theoretically to be a half-metallic ferromagnet. The low temperature transport measurements reported here are interpreted in terms of this model.