Synthesis mechanism and magnetoresistance effect of millimeter-sized GeTe faceted crystals

Abstract

GeTe materials have a wide range of applications in the fields of thermoelectrics, phase-change switching or storage, ferroelectrics, spintronics, and so on. In this paper, millimeter-sized GeTe faceted crystals are synthesized through heterogeneous chemical reactions without metal catalysts or transport agents. Most of the crystals have hexagonal surfaces, while a few crystals have rectangular surfaces, which are dominated by the closest packed (111) planes and the low-energy (100) planes, respectively. The 180° and 141°/39° ferroelectric domain walls are found on the (111) plane of hexagonal GeTe crystals by the chemical etching. By studying the products under different conditions, it's inferred that the GeTe faceted crystals are grown below the melting point by the reactions of preferentially deposited Ge motes and Te2/GeTe2 vapor phase, which are caused by the partial dissociation of polycrystalline GeTe. Hexagonal GeTe crystals with (111) plane exhibit non-saturating linear magnetoresistance (MR) of ∼25.9% under 9 T at 4.2 K, but the MR of rectangular crystals with (100) plane is just ∼9.5%. The MR effect of GeTe is likely related to the spin splitting on band structure due to the Rashba effect and the intrinsic inhomogeneity of telluride because of the heavily self-doped characteristic.