Theory on the Itinerant Ferromagnetism in the $3d$-transition metal systems

TL;DR

This paper develops a generalized theoretical framework to understand itinerant ferromagnetism in 3d transition metals, emphasizing the roles of band degeneracy, Hund's-rule coupling, and density of states features.

Contribution

It introduces a generalized Gutzwiller approximation incorporating band degeneracy and Hund's-rule coupling to explain ferromagnetism in 3d transition metals.

Findings

Both Hund's-rule coupling and density of states features are essential for ferromagnetism.

Phase diagrams illustrate the interplay between band shape and Hund's coupling.

The theory explains incomplete ferromagnetism in cobalt and iron.

Abstract

Keeping nickel, cobalt and iron in mind, we investigate the origin of the itinerant ferromagnetism. In so doing, we generalize the Gutzwiller approximation. In that,we take account of the effect of the band degeneracy and the Hund's-rule coupling in addition to the on-site repulsion. After the discussion on nickel, the condition for the incomplete ferromagnetism, observed in cobalt and iron, is argued. Phase diagrams, which show the interplay between the band shape peculiarity and the Hund's-rule coupling, are given. It is found that for the $3d$-transition metal systems, both of the Hund's-rule coupling and the special feature of the density of states are necessary to explain the itinerant ferromagnetism.