Itinerant ferromagnetism in the multiorbital Hubbard model: a dynamical mean-field study

TL;DR

This study uses dynamical mean-field theory with an improved quantum Monte Carlo method to investigate how lattice structure and Hund's coupling influence itinerant ferromagnetism in multiorbital Hubbard models, revealing their essential roles.

Contribution

It demonstrates the importance of lattice structure and orbital degeneracy in stabilizing ferromagnetism, highlighting the significance of Hund's coupling and correlation effects beyond the Stoner model.

Findings

Both lattice structure and orbital degeneracy are crucial for ferromagnetism.

Hund's coupling significantly influences ferromagnetic stability.

Ferromagnetism arises from correlation effects, not just band-filling.

Abstract

In order to resolve the long-standing issue of how the itinerant ferromagnetism is affected by the lattice structure and Hund's coupling, we have compared various three-dimensional lattice structures in the single- and multiorbital Hubbard models with the dynamical mean-field theory with an improved quantum Monte Carlo algorithm that preserves the spin-SU(2) symmetry. The result indicates that {\it both} the lattice structure and the d-orbital degeneracy are essential for the ferromagnetism in the parameter region representing a transition metal. Specifically, (a) Hund's coupling, despite the common belief, is important, which is here identified to come from particle-hole scatterings, and (b) the ferromagnetism is a correlation effect (outside the Stoner picture) as indicated from the band-filling dependence.