Bipolar-like Effect and its Suppression in Magnetic Thermoelectrics GeMnTe2

Bipolar effect is a common negative factor for the optimization of thermoelectric materials. Usually, it can be suppressed by enlarging the band gap or increasing the concentration of the majority carrier. Here, we report the anomalous bipolar-like effect and its suppression in GeMnTe2, an emerging thermoelectrics with narrow band gap and high carrier concentration. By introducing extra Sb doping, the transport inflection points induced by the bipolar-like effect are removed, accompanied by the decrease of the carrier concentration. Based on the X-ray diffraction and magnetic susceptibility measurements, the anomalous effect is attributed to the magnetic interaction rather than the competition between the majority and minority carriers. Owing to the suppression of the bipolar-like effect and optimization of carrier concentration, the peak zT of GeMnTe2 is significantly enhanced from 0.6 to 1.3 at 823 K.