Phase diagram and electronic structure of Ni2+xMn1-xGa

We determine the phase diagram of Ni2+xMn1-xGa as a function of x (0 < x <= 0.35) from ac susceptibility and differential scanning calorimetry (DSC). Total energy and density of states calculated using the ab initio full potential linearized plane-wave (FPLAPW) method explain the phase diagram. A martensitic paramagnetic phase for x > 0.2 has been identified. The structure of this phase is found to be tetragonal from high-temperature x-ray-diffraction (XRD) studies. XRD, magnetization, and DSC measurements show that the paramagnetic tetragonal phase evolves from the lower temperature ferromagnetic tetragonal phase through a second-order phase transition without any change of structure. The unoccupied conduction band has been studied by inverse photoemission spectroscopy. It is dominated by Mn 3d-like states, and is in good agreement with FPLAPW based calculations.