Magnetic order and electrical conductivity scaling of the spinel oxide Mn0.5Ru0.5Co2O4

We report the magnetic order and electrical (ac and dc) conductivity of bulk Mn0.5Ru0.5Co2O4 spinel oxide. The system is a ferrimagnet, which undergoes from ferrimagnetic to paramagnetic state above the Curie temperature (T-C)similar to 100 K. Low field (<= 100 Oe) measurement shows a peak at T-p approximate to 100 K in zero field cooled (ZFC) magnetization, whereas field cooled magnetization continuously increases down to 2 K. As long as the applied magnetic field is not large enough in comparison with the coercive field, a sharp decrease in ZFC magnetization is always observed below T-p. The peak temperature at T-p approximate to 100 K is shifted to lower temperatures by applying sufficiently large magnetic field. ac susceptibility (chi' and chi") also shows a sharp peak at 100 K, which is independent of frequencies (0.5 Hz-1 kHz) of ac magnetic field (amplitude similar to 1 Oe). These observations, including other measurements, suggest strong pinning effects in domain wall dynamics. We have noted that electrical behavior of the system is significantly affected by the magnetic ordering of the spins. Our results have shown the contribution of short range interactions above T-C to the formation of small polarons. The system shows colossal magnetoresistance properties with a semiconductor to metallic transition below 80 K. A simple scaling law is used as a tool for the identification of short range magnetic interactions that may be difficult to determine using conventional magnetization experiments.