CoFeVSb: A promising candidate for spin valve and thermoelectric applications

We report a combined theoretical and experimental study of a novel quaternary Heusler system, CoFeVSb, from the viewpoint of room-temperature spintronics and thermoelectric applications. CoFeVSb crystallizes in a cubic structure with a small $\mathrm{D}{\mathrm{O}}_{3}$-type disorder. The presence of the disorder is confirmed by room-temperature synchrotron x-ray diffraction and extended x-ray absorption fine structure measurements. Magnetization data reveal a high ordering temperature $(\ensuremath{\sim}850\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ with a saturation magnetization of 2.2 ${\ensuremath{\mu}}_{B}/\mathrm{f}.\mathrm{u}.$ Resistivity measurements indicate a half-metallic or semimetallic nature. A double hysteresis loop along with asymmetry in the magnetoresistance data reveals a room-temperature spin valve feature, which remains stable even at 300 K. Hall measurements show anomalous behavior with a significant contribution from the intrinsic Berry phase. This alloy also has a large room-temperature power factor ($\ensuremath{\sim}0.62 \mathrm{mW}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}$) and ultralow simulated lattice thermal conductivity ($\ensuremath{\sim}0.4 \mathrm{W}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$), making it a promising candidate for thermoelectric application. Ab initio calculations suggest weak spin-polarized semimetallic behavior and reduced magnetization (in agreement with the experiment) in the presence of $\mathrm{D}{\mathrm{O}}_{3}$ disorder. We have also found an energetically competing ferromagnetic (FM)/antiferromagnetic interface structure within an otherwise FM matrix, one of the prerequisites for spin valve behavior. The coexistence of so many promising features in a single system is rare, and hence CoFeVSb gives a fertile platform to explore numerous applications in the future.