Synthesis of topological ferromagnet Fe3-xGeTe2 single crystals for thermoelectric applications

Magnetic topological materials have generated a lot of interest for their spin- and orbital-dependent electronic functionalities. The large Nernst Seebeck coefficient shown by the topological ferromagnets, even in moderate magnetic fields, makes them potential candidates for thermoelectric applications [1]. Here we report the synthesis of single crystals of the topological ferromagnet Fe3-xGeTe2. The compounds were synthesized using the standard self-flux based crystal growth. The elemental reagents were mixed with an excess of Ge and Te, then sealed in an evacuated quartz tube and heat-treated for several days, wherein crystals grow out of the flux during the slow cooling step. X-ray diffraction (XRD) confirms that crystals of the Fe3-xGeTe2 phase have been synthesized. The FeGe and FeTe2 impurity phases were also seen in XRD pattern. The compound crystallizes in the hexagonal P63/mmc space group. Temperature-dependent magnetic measurements show a ferromagnetic transition at TC~145K. The transition temperature increases with increase of Fe content in composition, and by controlling the Fe content we can tune the transition temperature up to ~250K. The comparison of transition temperature with an earlier report [2] suggests that the Fe~2.70GeTe2 composition was achieved (not yet confirmed by energy-dispersive X-ray spectroscopy analysis). Isothermal magnetization loop measurements demonstrated a soft-magnetic nature. Thermo-magnetic and thermoelectric measurements are underway and will be presented and discussed.