Lifshitz phase transitions in the ferromagnetic regime of the Kondo lattice model

TL;DR

This paper maps the low-temperature phase diagrams of spin-1/2 and spin-1 Kondo lattice models, revealing multiple ferromagnetic phases separated by Lifshitz transitions, and shows coexistence of ferromagnetism and Kondo screening.

Contribution

It provides the first detailed phase diagrams of these models highlighting Lifshitz transitions and coexistence of ferromagnetism and Kondo screening.

Findings

Multiple ferromagnetic phases separated by Lifshitz transitions.

Identification of a half-metal phase with a true gap in the minority band.

Coexistence of ferromagnetism and Kondo screening in the models.

Abstract

We establish the low-temperature phase diagrams of the spin-1/2 and spin-1 Kondo lattice models as a function of the conduction-band filling n and the exchange coupling strength J in the regime of ferromagnetic effective exchange interactions (n ~< 0.5). We show that both models have several distinct ferromagnetic phases separated by continuous Lifshitz transitions of the Fermi-pocket vanishing or emergence type: one of the phases has a true gap in the minority band (half metal), the others only a pseudogap. They can be experimentally distinguished by their magnetization curves; only the gapped phase exhibits magnetization rigidity. We find that, quite generically, ferromagnetism and Kondo screening coexist rather than compete, both in spin-1/2 and spin-1 models. We compute the Curie temperatures and establish a "ferromagnetic Doniach diagram" for both models.