We determine the phase diagram of ${\mathrm{Ni}}_{2+x}{\mathrm{Mn}}_{1-x}\mathrm{Ga}$ 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.

• Received 28 November 2005

DOI:https://doi.org/10.1103/PhysRevB.74.085110