Polaronic transport and thermoelectricity in Mn$_3$Si$_2$Te$_6$ single crystals

TL;DR

This study reveals polaronic transport, ferrimagnetic transition, and significant thermoelectric effects in Mn$_3$Si$_2$Te$_6$ single crystals, highlighting strong spin-lattice coupling and potential for thermoelectric applications.

Contribution

It provides a comprehensive analysis of structural, magnetic, and transport properties, demonstrating polaronic transport and magnetic field effects in Mn$_3$Si$_2$Te$_6$ for the first time.

Findings

Polaronic transport indicated by discrepancy in activation energies.

Large negative magnetoresistance of -87% at T_c.

Low thermal conductivity suppressed by magnetic field.

Abstract

We carried out a comprehensive study of the structural, electrical transport, thermal and thermodynamic properties in ferrimagnetic Mn$_3$Si$_2$Te$_6$ 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 $T_c$ $\sim$ 74 K, which is further confirmed by the specific heat measurement. Mn$_3$Si$_2$Te$_6$ exhibits semiconducting behavior along with a large negative magnetoresistance of -87\% at $T_c$ and relatively high value of thermopower up to $\sim$ 10 mV/K at 5 K. Besides the rapidly increasing resistivity $\rho(T)$ and thermopower $S(T)$ below 20 K, the large discrepancy between 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 Mn$_3$Si$_2$Te$_6$ is notably rather low, comparable to Cr$_2$Si$_2$Te$_6$, and is strongly suppressed in magnetic field across $T_c$, indicating the presence of strong spin-lattice coupling, also similar with Cr$_2$Si$_2$Te$_6$.