Vacancy induced structural and magnetic transition in MnCo1−xGe

The authors report ab initio total energy calculations on the first-order structural transition of the ferromagnetic MnCo1−xGe(0.00⩽x⩽0.25) intermetallic compound. They show that increasing Co vacancies induce a transition from an orthorhombic structure at 0⩽x⩽0.08 to a hexagonal structure at x>0.08. A concomitant high-to-low moment magnetic transition and a large magnetovolume effect occur due to the change of the symmetry and the resulting coupling distance between the magnetic atoms. These results provide an excellent account for the experimental results and reveal the crucial role of the Co vacancies in determining the relative structural stability and the magnetic properties of MnCo1−xGe.