Observation of conflicting Seebeck coefficient and Hall coefficient in Sb-doped MnBi4Te7 crystals

In the past decades, great efforts have been devoted to designing and developing high-efficiency thermoelectric (TE) materials due to the increasing demands in the fields of power generation, cooling, and sensing. Given that the developments of TE materials based on charge and phonon engineering are facing a plateau, the manipulation of spin degree of freedom has been considered as an innovative strategy to further improve the TE performance, which has drawn growing attention in recent years. In this work, we studied the thermoelectric transport properties of Sb-doped MnBi4Te7 crystals, which contain the Bi2Te3 layers for charge transport and MnTe layers for spins. We observed abnormally low thermopower in the crystals with Sb doping ratios of 0.25 and 0.35, and the sign of thermopower is contradictory to the Hall coefficient. Further experiments evidenced magnetic field-enhanced thermopower and electrical resistivity over a wide temperature range, which support a spin-driven thermoelectric mechanism. An explanation based on the interplay between the spin and heat in entropy transport via charged carriers is proposed.