Half-Metallicity and Slater-Pauling Behavior in the Ferromagnetic Heusler Alloys

Abstract

A significant number of the intermetallic Heusler alloys have been predicted to be half-metals. In this contribution we present a study of the basic electronic and magnetic properties of both Heusler families; the so-called half-Heusler alloys like NiMnSb and the the full-Heusler alloys like Co2MnGe. Based on ab-initio results we discuss the origin of the gap which is fundamental for the understanding of their electronic and magnetic properties. We show that the total spin magnetic moment Mt scales linearly with the number of the valence electrons Zt, such that Mt = Zt - 24 for the full Heuslers and Mt = Zt - 18 for the half Heuslers, thus opening the way to engineer new half-metallic alloys with the desired magnetic properties. Although at the surfaces and interfaces the half-metallic character is in general lost, we show that for compounds with Cr as the metallic element the large enhancement of the Cr surface moment can lead to a high polarization at the surface. Moreover we discuss the role of the spin-orbit coupling, which in principle destroys the half-metallic gap, but in practice only slightly reduces the 100% spin polarization at EF.