Anomalous transport in half-metallic ferromagnetic CrO2

We have investigated transport properties of CrO2 thin films deposited on TiO2 and sapphire substrates. The films are good metals down to low temperatures. The residual resistivity is of the order of 6 micro-ohhmcm for films deposited on TiO2 and two times higher for films on sapphire substrates. The sign of the magnetoresistance (MR) changes from negative to positive at a temperature around 100 K. This fact, as well as a rapid change in the ordinary and anomalous Hall coefficients suggest a change in the electronic state. At lower temperatures the MR is a linear function of the applied field. This linear dependence might be explained as intergrain tunneling MR. This interpretation is also suggested by the angular MR. The planar Hall effect measurements reveal that the CrO2 thin films are not in a single magnetic domain state even for films deposited on an isostructural TiO2 substrate.