First-Principles Study of Itinerant-Electron Magnets: Ground State and Thermal Properties

Abstract

We briefly review modern applications of density-functional theory for studies of both ground state magnetic structures and finite-temperature properties of itinerant-electron magnets. In the first part we deal with first-principles calculations of complex non-collinear magnetic structures taking as examples spiral structures like those found experimentally in fcc-Fe, the non-collinear magnetic states in U compounds and weak ferromagnetism in α-Fe203 and Mn3Sn. We show that these different phenomena are explained by means of a single theoretical approach. In the second part we describe a statistical mechanics scheme which is based essentially on using total-energy parameters obtained from first-principles calculations for particular non-collinear magnetic structures. This information is used to model spin fluctuations that determine the thermal properties of itinerant-electron magnets. As an example we determine the magnetic phase diagram of cobalt and show how the hcp—fcc phase transition can be described in terms of spin fluctuations. Furthermore, we explain the antiferromagnetic—to—ferromagnetic phase transition of FeRh by spin fluctuations obtaining the transition temperature as well as the Curie temperature in good agreement with experiment.