Localization versus delocalization of d-states within the $$\hbox {Ni}_{{2}}$$MnGa Heusler alloy

Abstract

We present calculations based on density-functional theory with improved exchange-correlation approaches to investigate the electronic structure of $$\hbox {Ni}_2$$ Ni 2 MnGa magnetic shape memory alloy prototype. We study the effects of hybrid functionals as well as a Hubbard-like correction parameter U on the structural, electronic and magnetic properties of the alloy. We show that the previously successful application of U on Mn should be extended by including U on Ni to describe the d localized electrons more accurately and in better agreement with experiments. The bonding interactions within this intermetallic alloy are analysed including the role of non-transition metal. We found that the strongest and most stabilizing bond is formed between the Ga–Ni pairs due to the delocalized s–s and p–s orbital hybridization. Our findings suggest that minimization of the over-delocalization error introduced by standard semi-local exchange-correlation functionals leads to a better description of the $$\hbox {Ni}_2$$ Ni 2 MnGa alloy. Furthermore we propose that the experimental total magnetic moment of Ni–Mn–Ga alloys could be increased after carefully selected heat treatment procedures.

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

“…S9 of the SM [61]). However, larger U Mn and U Ni values of 1.8 to ∼4 eV reported in literature [69][70][71] disagree with the experimental VB spectrum as well as the reported saturation magnetization values (4.04 − 4.27 μ B ) [60,[72][73][74] (see Note C and Figs. S9 and S10 of the SM [61]).…”

“…The excellent agreement in the DS between experiment and the theory for the MDL-R/S structures show the role of the periodic atomic modulation in achieving the CDW state. Our calculations indicate that GGA is adequate for describing the electronic structure of Ni 2 MnGa if the correct structure is considered and large values of U (1.8 to ∼4 eV) suggested recently [69][70][71] contradict the experimental results. Our paper establishes the electronic origin and the role of the atomic modulation in hosting the CDW state in the martensite phase of stoichiometric Ni 2 MnGa and resolves a recently generated controversy [29,30,69].…”