Ultraviolet-photoemission (UPS) measurements and supporting specific-heat, thermal-expansion, resistivity, and magnetic-moment measurements are reported for the magnetic shape-memory alloy ${\mathrm{Ni}}_2\mathrm{MnGa}$ over the temperature range $100<T<250\mathrm{K}$. All measurements detect clear signatures of the premartensitic transition ($T_{\mathrm{PM}}\sim 247\mathrm{K}$) and the martensitic transition ($T_M\sim 196\mathrm{K}$). Temperature-dependent UPS shows a dramatic depletion of states (pseudogap) at $T_{\mathrm{PM}}$ located 0.3 eV below the Fermi energy. First-principles electronic structure calculations show that the peak observed at 0.3 eV in the UPS spectra for $T>T_{\mathrm{PM}}$ is due to the Ni $d$ minority-spin electrons. Below $T_M$ this peak disappears, resulting in an enhanced density of states at energies around 0.8 eV. This enhancement reflects Ni $d$ and Mn $d$ electronic contributions to the majority-spin density of states.

• Received 28 January 2008

DOI:https://doi.org/10.1103/PhysRevLett.100.165703