Title: Magnetotransport and the spin state of FeSb2
Abstract: Motivated by the recent discovery of metallic surface states in the d-electron Kondo insulator candidates FeSi and FeSb2, along with some recent reports of magnetic correlations in the surface transport properties of FeSi, we have investigated the low temperature surface magnetotransport properties of FeSb2. By using a Corbino disk transport geometry, we were able to isolate the electrical transport properties of a single surface of our samples and study the [110] and [101] naturally forming faces separately. Studying the relationship between the applied magnetic field, current direction and crystal symmetry have allowed us to separate possible contributions to the magnetotransport anisotropy. Unlike previous study of SmB6 surface states, we find no 2D Drude-like dependence on current-field direction but instead magnetocrystalline anisotropy that appears to originate from local moment scattering with a well defined easy-axis along the [100] direction. We compare these results with results from probing the magnetotransport properties of the conducting surface states on the [111] facet of FeSi. We also find evidence of 3D variable-range hopping conduction at the bulk-to-surface crossover, extending below 1K, which implies that the electrical transport at the surface of these materials is carried by a thin 3D conducting layer. This 3D surface conduction channel is inconsistent with the lower dimensional states expected for a 3D topological insulator. In conjunction with the magnetic correlations found surface magnetotransport, we also attempt to probe the surface magnetic susceptibility of FeSb2 as well as the evolution of this magnetotransport anisotropy into the bulk of the material as we introduce magnetic order into the bulk of FeSb2 with chemical substitution.Â