Localization versus delocalization of d-states within the Ni2MnGa Heusler alloy

Abstract

We present calculations based on density-functional theory with improved exchange-correlation approaches to investigate the electronic structure of 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 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.