Electronic structure of the altermagnet candidate FeSb2: High-field torque magnetometry and density functional theory studies

This study explores the synthesis and electronic structure of ${\mathrm{FeSb}}_{2}$, an altermagnet (AM) candidate, through torque magnetometry and ab initio density functional theory calculations. The temperature-dependent magnetic susceptibility data reveal an antiferromagnetic ground state below room temperature. To probe its electronic properties, we conducted high-field torque magnetometry up to 41 T and observed clear de Haas--van Alphen (dHvA) oscillation with a major peak at 65 T. Angular and temperature-dependent dHvA measurements were further conducted to map the Fermi surface parameters of ${\mathrm{FeSb}}_{2}$. Interestingly, the spin-polarized electronic bands display asymmetric behavior between spin-up and spin-down states. The presence of a nonrelativistic spin splitting band in the collinear antiferromagnet depicted a strong evidence of altermagnetism in ${\mathrm{FeSb}}_{2}$. Three bands intersect the Fermi level, forming the Fermi surface of ${\mathrm{FeSb}}_{2}$. The band-resolved Fermi pockets exhibit $d$-wave symmetry and display asymmetry between the spin-up and spin-down states. These findings provide valuable insights into the electronic and magnetic structure of ${\mathrm{FeSb}}_{2}$ and strongly support its classification as an AM.