Phase diagram and electronic structure of Ni_2+xMn_1−xGa

Abstract

We determine the phase diagram of Ni_2+xMn_1−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 3 d -like states, and is in good agreement with FPLAPW based calculations.