Combined experimental and theoretical investigation of the premartensitic transition in Ni2MnGa

Abstract

Ultraviolet-photoemission (UPS) measurements and supporting specific-heat, thermal-expansion, resistivity, and magnetic-moment measurements are reported for the magnetic shape-memory alloy Ni2MnGa over the temperature range 100<T<250K. All measurements detect clear signatures of the premartensitic transition (TPM∼247K) and the martensitic transition (TM∼196K). Temperature-dependent UPS shows a dramatic depletion of states (pseudogap) at TPM 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>TPM is due to the Ni d minority-spin electrons. Below TM 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. © 2008 The American Physical Society.