Electronic topological transition and noncollinear magnetism in compressed hcp Co

Recent experiments showed that Co undergoes a phase transition from the ferromagnetic hcp phase to the nonmagnetic fcc one around 100 GPa. Since the transition is of first order, a certain region of coexistence of the two phases is present. By means of ab initio calculations, we found that the hcp phase itself undergoes a series of electronic topological transitions (ETTs), which affects both elastic and magnetic properties of the material. Most importantly, we propose that the sequence of ETTs lead to the stabilization of a noncollinear spin arrangement in highly compressed hcp Co. Details of this noncollinear magnetic state and the interatomic exchange parameters that are connected to it are presented here.