Combined Experimental and Theoretical Investigation of the Premartensitic Transition in Ni2 MnGa

Abstract

Ultraviolet-photoemission (UPS) measurements and supporting specific-heat, thermal-expansion, resistivity, and magnetic-moment measurements are reported for the magnetic shape-memory alloy Ni 2 MnGa over the temperature range 100 < T < 250 K . All measurements detect clear signatures of the premartensitic transition ( T PM ∼ 247 K ) and the martensitic transition ( T M ∼ 196 K ). Temperature-dependent UPS shows a dramatic depletion of states (pseudogap) at T 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 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.