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 SrMnSb (y, z < 0.1) with nearly massless relativistic fermion behaviour (m =  0.04 - 0.05m, where m 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 SrMnSb offers a rare opportunity to investigate the interplay between relativistic fermions and spontaneous TRS breaking.

The extraordinary properties of two dimensional (2D) materials, such as the extremely high carrier mobility 1,2 in graphene and the large direct band gaps in transition metal dichalcogenides MX 2 (M = Mo or W, X = S, Se) monolayers 3 , highlight the crucial role quantum confinement can have in producing a wide spectrum of technologically important electronic properties. Currently one of the highest priorities in the field is to search for new 2D crystalline systems with structural and electronic properties that can be exploited for device development. In this letter, we report on the unusual quantum transport properties of the 2D ternary transition