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 (MnV sub(2)O sub(4), FeV sub(2)O sub(4), CoV sub(2)O sub(4), and Mn sub(3)O sub(4)) upon varying the temperature and magnetic field. We found that for the spinel oxides having V super(3+) ions (two electrons in the t sub(2g) 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 t sub(2g) states is the main factor affecting the thermal conductivity. On the other hand, for Mn sub(3)O sub(4), which has Mn super(3+) ions (one electron in the e sub(g) states) at the octahedral site, the thermal resistivity is suppressed in association with the successive magnetic phase transition with decreasing temperature and increasing magnetic field. This can be explained by the frustration of Mn super(3+) spins and the fluctuation of Mn super(3+) e sub(g) orbitals.