Weak ferromagnetism with the Kondo screening effect in the Kondo lattice systems

TL;DR

This paper investigates the coexistence of ferromagnetism and Kondo screening in Kondo lattice systems, revealing a phase diagram with distinct ferromagnetic phases and a transition to a paramagnetic state, explaining recent experimental observations.

Contribution

It provides a comprehensive mean-field phase diagram showing coexistence of ferromagnetism and Kondo screening, including new polarized phases and phase transitions.

Findings

Identification of two ferromagnetic phases with Kondo screening: fully and partially polarized.

Existence of a continuous phase transition to a paramagnetic heavy Fermi liquid.

Explanation of weak ferromagnetism in Kondo lattice materials.

Abstract

We carefully consider the interplay between ferromagnetism and the Kondo screening effect in the conventional Kondo lattice systems at finite temperatures. Within an effective mean-field theory for small conduction electron densities, a complete phase diagram has been determined. In the ferromagnetic ordered phase, there is a characteristic temperature scale to indicate the presence of the Kondo screening effect. We further find two distinct ferromagnetic long-range ordered phases coexisting with the Kondo screening effect: spin fully polarized and partially polarized states. A continuous phase transition exists to separate the partially polarized ferromagnetic ordered phase from the paramagnetic heavy Fermi liquid phase. These results may be used to explain the weak ferromagnetism observed recently in the Kondo lattice materials.