Second-order tunneling in half-metallic CrO2 grain pellets

The magnetoresistance (MR) of cold-pressed powder pellets of the half-metallic ferromagnet CrO2 was measured in wide ranges of temperature T and magnetic fields H up to μ0H=16 T. The MR increases from 2% at 300 K up to 64% at T=1.5 K and no saturation is observed up to 16 T. The low field resistivity depends logarithmically on temperature whereas the high-field MR shows a scaling behavior with H/T. The results favor second-order tunneling (paramagnetic assisted tunneling) at zero bias via localized magnetic moments at or within the barrier between the CrO2 grains as the dominant resistivity mechanism for both the low- and high-field MR, respectively.