A magnetic topological semimetal Sr1−yMn1−zSb2 (y, z < 0.1)

Weyl (WSMs) evolve from Dirac semimetals in the presence of broken time-reversal symmetry (TRS) or space-inversion symmetry. The WSM phases in TaAs-class materials and photonic crystals are due to the loss of space-inversion symmetry. For TRS-breaking WSMs, despite numerous theoretical and experimental efforts, few examples have been reported. In this Article, we report a new type of magnetic semimetal Sr_1−yMn_1−zSb₂ (y, z < 0.1) with nearly massless relativistic fermion behaviour (m^∗ =  0.04 − 0.05m₀, where m₀ is the free-electron mass). This material exhibits a ferromagnetic order for 304 K  <  T  <  565 K, but a canted antiferromagnetic order with a ferromagnetic component for T  <  304 K. The combination of relativistic fermion behaviour and ferromagnetism in Sr_1−yMn_1−zSb₂ offers a rare opportunity to investigate the interplay between relativistic fermions and spontaneous TRS breaking.