First-principles electronic structure of shape-memory alloy Ni$_2$MnGa

The Ni$_2$MnGa memory-shape alloy undergoes both a feromagnetic phase trasition (T$_C$~$\sim$~380~K) and a martensitic transformation (MT, T$_M$~$\sim$~175~K) upon cooling. In addition, the MT is preceeded by a premartensitic (pre-MT) phase transition corresponding to a micromodulated structure accompanied by phonon softening presumably related to Fermi-surface nesting and strong electron-phonon coupling. Here, we report results of a comparison study of first-principles electronic structure calculations and recent angle-resolved photoemission measurements, at temperatures T=219~K, in close proximity with the pre-MT, and T=173~K, in the martensite phase.