Microscopic conditions favoring itinerant ferromagnetism

TL;DR

This paper uses quantum Monte Carlo simulations within dynamical mean-field theory to identify microscopic conditions, such as spectral weight distribution and correlations, that stabilize itinerant ferromagnetism in a single-band model.

Contribution

It provides a systematic analysis of the microscopic factors, including the role of spectral features and correlations, influencing the stability of itinerant ferromagnetism at finite temperatures.

Findings

A peak in the density of states near the band edge stabilizes ferromagnetism.

Correlation effects are crucial for accurate transition temperature predictions.

Nearest-neighbor Heisenberg exchange is generally not decisive.

Abstract

A systematic investigation of the microscopic conditions stabilizing itinerant ferromagnetism of correlated electrons in a single-band model is presented. Quantitative results are obtained by quantum Monte Carlo simulations for a model with Hubbard interaction U and direct Heisenberg exchange interaction F within the dynamical mean-field theory. Special emphasis is placed on the investigation of (i) the distribution of spectral weight in the density of states, (ii) the importance of genuine correlations, and (iii) the significance of the direct exchange, for the stability of itinerant ferromagnetism at finite temperatures. We find that already a moderately strong peak in the density of states near the band edge suffices to stabilize ferromagnetism at intermediate U-values in a broad range of electron densities n. Correlation effects prove to be essential: Slater--Hartree-Fock results for the transition temperature are both qualitatively and quantitatively incorrect. The nearest-neighbor Heisenberg exchange does not, in general, play a decisive role. Detailed results for the magnetic phase diagram as a function of U, F, n, temperature T, and the asymmetry of the density of states are presented and discussed.