Combined experimental and theoretical investigation of the premartensitic transition in Ni2MnGa.
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<250 K. All measurements detect clear signatures of the premartensitic transition (T(PM) approximately 247 K) and the martensitic transition (T(M) approximately 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.
Opeil
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CP
Physics Department, Boston College, 140 Commonwealth Avenue, Chestnut Hill, Massachusetts 02467, USA.
Mihaila
B
B
Schulze
R K
RK
Mañosa
L
L
Planes
A
A
Hults
W L
WL
Fisher
R A
RA
Riseborough
P S
PS
Littlewood
P B
PB
Smith
J L
JL
Lashley
J C
JC