Magnetism Modulation for Cryogenic Thermoelectric Enhancements in Fe₃O₄ Nanoparticle-Incorporated Bi_0.85Sb_0.15 Nanocomposites

The internal magnetism introduced by the magnetic nanoparticles combined with the external magnetic field can provide an effective way to modulate the thermoelectric (TE) properties of materials. Herein, we comparably investigate the effect of magnetism of Fe 3 O 4 nanoparticles (Fe 3 O 4 -NPs) and the external magnetic field on the cryogenic thermoelectric properties of Fe 3 O 4 -NP/Bi 0.85 Sb 0.15 nanocomposites. With the ferromagnetism–superparamagnetism transition, the Fe 3 O 4 -NPs in the superparamagnetic state exhibit a stronger magneto-trapped carrier effect, where the electron concentration at high temperature is evidently reduced. With the simultaneous increase of S and reduction of electronic thermal conductivity, a high ZT value of 0.33 at 180 K is obtained for 0.05 wt % Fe 3 O 4 /Bi 0.85 Sb 0.15 . Meanwhile, under the external magnetic field, the magnetoresistance of the composites is suppressed by Fe 3 O 4 -NPs, which results in a remarkable enhancement of the electronic transport performance. Consequently, the highest ZT value of 0.48 at 220 K under 1 T is achieved for 0.1 wt % Fe 3 O 4 -NPs/Bi 0.85 Sb 0.15, increased by 55% compared with that of the matrix. A single-leg device is prepared using 0.1 wt % Fe 3 O 4 -NP/Bi 0.85 Sb 0.15 nanocomposites. Its cooling temperature difference at 180 K reaches 1.3 and 3.2 K under 0 and 1 T when applying 300 mA current, increased by 20 and 46% compared with that of the matrix, respectively. This work suggests that magnetism modulation with introducing magnetic nanoparticles will enhance the TE and magneto-TE performance of composite materials.