ZnC*

We present first-principles calculations suggesting that the ferromagnetic phase of cubic antiperovskite Mn₃ZnC is a nodal line Weyl semimetal. Electronic structure features that are the hallmark of this nodal line state—a large density of linear band crossing near the Fermi level—can also be interpreted as signatures of structural and magnetic instability. In fact, it is known that Mn₃ZnC transitions upon cooling from a paramagnetic to a cubic ferromagnetic state under ambient conditions and then further into a non-collinear tetragonal phase at a temperature between 250 K and 200 K. The existence of Weyl nodes and their destruction via structural and antiferromagnetic ordering is likely relevant to a range of magnetostructurally coupled materials.