Nesting-driven ferromagnetism of itinerant electrons

TL;DR

This paper presents a theoretical study of a nested electron-hole system showing that doping induces ferromagnetism through a mechanism distinct from the Stoner model, with implications for magnetic phase behavior.

Contribution

It introduces a model demonstrating doping-induced ferromagnetism in nested Fermi surface systems, highlighting a non-Stoner mechanism and analyzing complex magnetic phases.

Findings

Doping induces ferromagnetism in the model.

The ground state without doping is insulating with density-wave order.

Various magnetic phases, including half-metallicity, are identified.

Abstract

We theoretically investigate a model with electrons and holes whose Fermi surfaces are perfectly nested. The fermions are assumed to be interacting, both with each other and with the lattice. To suppress inhomogeneous states, a sufficiently strong long-range Coulomb repulsion is included into the model. Using the mean field approximation, one can demonstrate that in the absence of doping, the ground state of such a model is insulating and possesses a density-wave order, either SDW, or CDW. Upon doping, a finite ferromagnetic polarization emerges. It is argued that the mechanism driving the ferromagnetism is not of the Stoner type. A phase diagram of the model is constructed, and various properties of the ordered phases, such as half-metallicity and cone magnetic structure, are studied.