Bulk electronic structure of Mn₂NiGa using hard x-ray photoelectron spectroscopy and density functional theory

Abstract

Mn2NiGa is a potential magnetic shape memory alloy with austenite to the martensite phase transition. Here, we have investigated the bulk electronic structure of Mn2NiGa in the austenite and martensite phases studying its valence band using hard x-ray photoelectron spectroscopy (HAXPES). In the austenite phase, we observe a wide (≈ 10 eV) valence band (VB) spectrum with several prominent features. In order to explain the HAXPES VB spectra, we have compared our experimental VB spectra with the theoretical VB calculated using the partial density of states from our existing density functional theory (DFT) calculations. The shape of the experimental VB and energy positions of all features are in excellent agreement with the calculated VB and we find that the former is dominated by Ni 3d as well as 4s states of Mn, Ni, and Ga. An important observation is that experimental VB combined with the DFT-based VB calculation establishes the prevalence of the anti-site disorder in Mn2NiGa. Compared to the austenite phase, in the martensite phase, the VB shows a marginal decrease in the density of states around -0.5 eV below the Fermi level (EF ), and the main peak is slightly shifted towards EF. These experimental observations have been explained by considering the tetragonally distorted structure with the anti-site disorder in the martensite phase.

Bulk electronic structure of Ni2MnGa studied by density functional theory and hard x-ray photoelectron spectroscopy

“…The DOS in Fig. S11 of the SM [61] demonstrates that antisite disorder does not alter the position of the features, although it does slightly broaden them, as was previously observed in other ternary materials [58,75] (see also Refs. [30][31][32] of the SM [61]).…”

“…This indicates that the recoil effect [65]-a phenomenon observed in HAXPES of light materials [66] as a shift of the photoemission peaks to higher binding energy-is not significant. In addition, as is the case for Ni 2 MnGa, the recoil effect has been reported to be insignificant for heavier 3d transition metal systems [52][53][54]58].…”

“…Due to the development of high-brilliance synchrotron sources working in the stable top-up mode [49], HAXPES has turned out to be a useful technique to probe the bulk electronic structure [50][51][52][53][54][55]. Although there are a few HAX-PES studies on other Heusler alloys [56][57][58], the only work on Ni-Mn-Ga system is a comparison of two non-stoichiometric compositions [59]. Thus, this paper is not related to our cur- rent investigation on stoichiometric Ni 2 MnGa in the austenite (300 K) and martensite phase (50 K) employing HAXPES and also DFT.…”