Magnetic order and electrical conductivity scaling of the spinel oxideMn0.5Ru0.5Co2O4

Abstract

We report the magnetic order and electrical (ac and dc) conductivity of bulk ${\mathrm{Mn}}_{0.5}{\mathrm{Ru}}_{0.5}{\mathrm{Co}}_{2}{\mathrm{O}}_{4}$ spinel oxide. The system is a ferrimagnet, which undergoes from ferrimagnetic to paramagnetic state above the Curie temperature $({T}_{C})\ensuremath{\sim}100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Low field $(\ensuremath{\leqslant}100\phantom{\rule{0.3em}{0ex}}\mathrm{Oe})$ measurement shows a peak at ${T}_{p}\ensuremath{\approx}100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in zero field cooled (ZFC) magnetization, whereas field cooled magnetization continuously increases down to $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. 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 ${T}_{p}\ensuremath{\approx}100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is shifted to lower temperatures by applying sufficiently large magnetic field. ac susceptibility (${\ensuremath{\chi}}^{\ensuremath{'}}$ and ${\ensuremath{\chi}}^{\ensuremath{''}}$) also shows a sharp peak at $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which is independent of frequencies $(0.5\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}--1\phantom{\rule{0.3em}{0ex}}\mathrm{kHz})$ of ac magnetic field (amplitude $\ensuremath{\sim}1\phantom{\rule{0.3em}{0ex}}\mathrm{Oe}$). 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 $80\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. 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.