Theory of Heusler and Full-Heusler Compounds

Abstract

Spintronics/magnetoelectronics brought at the center of scientific research the Heusler and full-Heusler compounds, since several among them have been shown to be half-metals. In this introductory chapter we present a study of the basic electronic and magnetic properties of both Heusler families; the so-called semi-Heusler alloys like NiMnSb and the full-Heusler alloys like Co\(_2\)MnGe (usual full-Heuslers), Mn\(_2\)CoAl (inverse full-Heuslers) and (CoFe)MnAl (LiMgPdSn-type full-Heuslers). First-principles calculations are employed to discuss the origin of the gap which is fundamental for the understanding of their electronic and magnetic properties. For half-metallic Heusler compounds the total spin magnetic moment \(M_t\) scales linearly with the number of the valence electrons \(Z_t\) in the unit cell. These simple rules connect directly the magnetic to the electronic properties opening the way to engineer new half-metallic alloys with “a la carte” magnetic properties such as the quaternary half-metals, the so-called half-metallic antiferromagnets, magnetic semiconductors or even the more exotic spin-gapless semiconductors. Finally, special topics like exchange constants, defects, vacancies, surfaces and interfaces are being discussed.