CrTe as a versatile thermoelectromagnetic multi-functional material

Abstract

Materials with large magnetocaloric effects and high thermoelectric performance are of fundamental interest to all-solid-state refrigeration technology. Herein, we report CrTe-based ferromagnetic semi-metals as an exceptional example showing both desirable magnetic entropy change (−ΔSM) and promising thermoelectric figure of merit (ZT) near room temperature. A proper amount (9 mol. %) of Cr deficiency is found to stabilize the hexagonal structure of CrTe. Cr0.91Te displays a maximum −ΔSM value of ∼2.4 J/Kg·K under an applied magnetic field of 5 T around its Curie temperature (TC) of 332 K and a strikingly large ZT value of 1.2 × 10−2 at 300 K (two to four orders of magnitude larger than any other ferromagnetic compounds reported so far). The exceptional thermoelectric performance in such a semi-metal is believed to originate from the inherently strong electron–phonon–spin interactions: magnon-drag effect mediated Seebeck coefficient enhancement and phonon–spin coupling induced thermal conductivity reduction. The introduction of antiferromagnetic CrSb not only systematically decreases TC of Cr0.91Te down to or even below room temperature but also boosts its thermoelectromagnetic properties. Specifically, Cr0.91Te0.9Sb0.1 obtains a maximum −ΔSM value of ∼2.6 J/Kg·K @ 5 T around TC = 315 K and a ZT value of 2.0 × 10−2 at 300 K, which represent 8% and 75% improvement over pristine Cr0.91Te, respectively. This research highlights the possibility of exploring ferromagnetic semi-metals as advanced thermoelectromagnetic multi-functional materials.