Temperature dependence of ac response in diluted half-metallic CrO2 powder compact

We present a study on temperature dependence of impedance spectra of the cold-pressed chromium dioxide (CrO2)-titanic dioxide (TiO2) composite over the temperature range of 77-300 K, and over the frequency range of 40 Hz-500 kHz. The microstructure of the sample is analyzed using transmission electron microscopy (TEM), SEM and X-ray diffraction (XRD). The impedance spectra exhibit a strong dependence upon temperature. By evaluating the ac electricity behavior of the composite, we find the experimental data are successfully described by a power-law behavior sigma(ac) = A (T)omega(s), in which the frequency exponent s shows slightly greater than a universal value (0 less than or equal to s less than or equal to 1), and rises approximately linearly with temperature over a broad range of low temperature. (C) 2004 Elsevier B.V. All rights reserved.