Motivated by the recent discovery of metallic surface states in the $d$-electron Kondo insulator candidates FeSi and ${\mathrm{FeSb}}_2$, 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 ${\mathrm{FeSb}}_2$. 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 has allowed us to separate possible contributions to the magnetotransport anisotropy. Unlike previous studies of ${\mathrm{SmB}}_6$ surface states, we find no two-dimensional Drude-like dependence on field orientation relative to current direction, but instead a 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 the magnetotransport properties of the conducting surface states on the [111] facet of FeSi. We also find evidence of three-dimensional variable-range-hopping conduction below the bulk-to-surface crossover, extending below 1 K, which implies that the electrical transport at the surface of these materials is carried by a thin but three-dimensional conducting channel, which is inconsistent with the lower dimensional states expected for a strong topological insulator.

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• Electrical conductivity
• Hopping transport
• Magnetic anisotropy
• Surface states
• Topological insulators
• Resistivity measurements