Theory of the half-metallic heusler compounds

Abstract

Multicomponent systems play a key role in materials design providing the multifunctionality and tunability of materials. At present, the ternary Heusler materials form probably the most thoroughly studied class of multicomponent systems. In present work, results of ab-initio band structure calculations for A 2 BC Heusler compounds that consist of A and B sites occupied by transition metals and C by a main group element are presented. These systems cover an extremely wide range of properties from half-metallic ferromagnets to non-magnetic semiconductors. The calculations have been performed in order to understand the properties of the band gap in the minority spin channel, the peculiar transport properties and magnetic behaviour found in these materials. Among the interesting aspects of the electronic structure of these materials are the contributions from both A and B atoms to the total magnetic moment. In several classes of these compounds the magnitudes of the total magnetic moment show a trend consistent with the Slater-Pauling behaviour. The total magnetic moment depends as well on the kind of C atoms although they do not directly contribute to it. In Co2 compounds, a change of the C element changes the contribution of the t 2g states to the moment at the Co sites. The localised moment in these magnetic compounds resides at the B site. Other than in the classical Cu2-based Heusler compounds, the A atoms in Co2-, Fe2- and Mn2-based compounds may contribute to the total magnetic moment significantly. It is shown that the inclusion of electron-electron correlation in the form of LDA+U/DMFT calculations helps to understand the magnetic properties of those compounds that exhibit already a minority gap in calculations where it is neglected. Beside the large group of Co2 compounds, half-metallic ferromagnetism was here found only in such compounds that contain Mn. In parallel we consider the different types of chemical disorder often accompanying multicomponent systems and characterise its influence on spin-polarisation and magnetic properties.