Comparative studies of the thermal conductivity of spinel oxides with orbital degrees of freedom

We studied the thermal conductivity of various transition-metal oxides with the spinel structure (MnV2O4, FeV2O4, CoV2O4, and Mn3O4) upon varying the temperature and magnetic field. We found that for the spinel oxides having V3+ ions (two electrons in the t2g states) at the octahedral site, the orbital ordering suppresses the thermal resistivity (inverse thermal conductivity) in contrast to purely magnetic ordering, indicating that the orbital fluctuation of the V t2g states is the main factor affecting the thermal conductivity. On the other hand, for Mn3O4, which has Mn3+ ions (one electron in the eg states) at the octahedral site, the thermal resistivity is suppressed in association with the successive magnetic phase transitions with decreasing temperature and increasing magnetic field. This can be explained by the frustration of Mn3+ spins and the fluctuation of Mn3+ eg orbitals.