Magnetic dichroism in the Kondo insulator SmB6

Samarium hexaboride (${\mathrm{SmB}}₆$) is a purported topological Kondo insulator, with theory predicting that the experimentally observed metallic surface states manifest from a topologically nontrivial insulating bulk band structure. The insulating bulk itself is driven by strong correlations, and both bulk and surface are known to host compelling magnetic and electronic phenomena. We employed x-ray absorption spectroscopy and x-ray magnetic circular dichroism at the Sm ${M}_4,5$ edges to probe the surface and bulk magnetic properties of ${\mathrm{Sm}}²⁺$ and ${\mathrm{Sm}}³⁺$ within ${\mathrm{SmB}}₆$. We observed an unexpected antialignment to the applied field of the ${\mathrm{Sm}}³⁺$ magnetic dipole moment below $T=75$ K and of the total orbital moment of samarium below 30 K. The total bulk magnetization at 2 K is, however, positive and driven by ${\mathrm{Sm}}²⁺$ Van Vleck susceptibility as well as 1% paramagnetic impurities with ${\ensuremath{\mu}}_{\mathrm{eff}}=5.2(1){\ensuremath{\mu}}_{\mathrm{B}}$. This indicates the diamagneticlike ${\mathrm{Sm}}³⁺$ magnetism is only a portion of the net magnetization, partially offsetting the response of paramagnetic impurities known within the bulk.