Double Exchange Ferromagnetism in the Peierls Insulator State

TL;DR

This paper investigates how band gap opening affects double exchange ferromagnetism in a one-dimensional model, revealing conditions under which ferromagnetism persists or is destroyed, leading to an insulator with ferromagnetic or antiferromagnetic order.

Contribution

It provides a detailed analysis of the transition from ferromagnetic to antiferromagnetic states driven by dimerization and gap opening in a one-dimensional double exchange model.

Findings

Peierls gap opens in the fully spin-polarized band without destroying ferromagnetism in weak dimerization.

Strong dimerization destroys ferromagnetism and induces antiferromagnetic order.

An insulator with double exchange ferromagnetism is established under certain conditions.

Abstract

We study the effects of opening of the band gap on the double exchange ferromagnetism. Applying the density-matrix renormalization group method and an analytical expansion from the dimer limit to the one-dimensional double exchange model, we demonstrate for a relevant region of the exchange coupling that, in the weak dimerization regime, the Peierls gap opens in the fully spin-polarized conduction band without affecting its ferromagnetism, whereas in the strong dimerization regime, the ferromagnetism is destroyed and the Mott gap opens instead, leading the system to the antiferromagnetic quasi-long-range order. An insulator version of the double exchange ferromagnetism is thus established.