Evidence for altermagnetic order in Cr-doped FeSb2

Abstract

Altermagnets are a class of materials with compensated magnetic moments, in which spin sublattices are related by specific symmetries other than inversion or translation. This allows time-reversal symmetry to be broken without a net magnetization. Here, we synthesize single crystals of Fe1-xCrxSb2 and investigate their electrical transport and magnetic properties, with a focus on Fe0.85Cr0.15Sb2. Magnetization measurements suggest spin-compensated ordering below ~ 3.5 K, where magnetic moments align along the crystallographic b-direction. Transport measurements reveal a crossover from large positive to negative magnetoresistance, while an anomalous Hall response emerges below 3.5 K, indicating time-reversal symmetry breaking below TN. Muon spin relaxation measurements demonstrate bulk magnetic order below 3.5 K, confirming that the low temperature ordering is intrinsic rather than due to an impurity phase. These results support a potential altermagnetic ground state in Cr-doped FeSb2 with time-reversal symmetry breaking without net magnetization.