Magnetic, transport, thermal properties and orbital state for spinel MnTi2O4

We systematically investigated the various properties of MnTi2O4. The compounds are found to be conducted by small polarons with different activation energies across the temperature T1 and deviate from the Curie–Weiss law for the magnetic susceptibility at T1. Also at T1 do the specific heat undergo a crossover. As indicated by the X-ray diffraction peaks, the series of phenomena near the characteristic temperature T1 are attributed to the happening of the micro-structural distortion, and the distortion implies the short-range orbital ordering state below T1. This short-range oribtal ordering state is supported by the little upturn of the thermal conductance at T1. As the temperature decreases, the systems enter a long-ranged collinear ferrimagnetic state at a lower temperature TN. Moreover, the compounds decreases in thermal-electric power with the decrease of temperature and undergoes a p-type to n-type transition at the temperature Tpn. Through the quantitative theoretical analysis, both the decrease of the thermal power and the p-type to n-type transition are cooperatively induced by spin–orbit (SO) coupling and the Jahn–Teller (JT) effect.