Polaronic transport and thermoelectricity in Mn3Si2Te6 single crystals

We carried out a comprehensive study of the structural, electrical transport, thermal, and thermodynamic properties in ferrimagnetic Mn3Si2Te6 single crystals. Mn and Te K-edge x-ray absorption spectroscopy and synchrotron powder x-ray diffraction were measured to provide information on the local atomic environment and the average crystal structure. The dc and ac magnetic susceptibility measurements indicate a second-order paramagnetic to ferrimagnetic transition at T-c similar to 74 K, which is further confirmed by the specific heat measurement. Mn3Si2Te6 exhibits semiconducting behavior along with a large negative magnetoresistance of -87% at T-c and a relatively high value of thermopower up to similar to 10 mV/K at 5 K. Besides the rapidly increasing resistivity rho(T) and thermopower S(T) below 20 K, the large discrepancy between the activation energy for resistivity E-rho and thermopower E-S above 20 K indicates the polaronic transport mechanism. Furthermore, the thermal conductivity kappa(T) of Mn3Si2Te6 is notably rather low, comparable to Cr2Si2Te6, and is strongly suppressed in the magnetic field across T-c, indicating the presence of strong spin-lattice coupling, also similar with Cr2Si2Te6.