Kondo lattice model with a direct exchange interaction between localized moments

TL;DR

This paper investigates the effects of direct exchange interactions in the Kondo lattice model, revealing phase transitions, critical behavior, and explaining experimental observations related to Kondo temperature minima.

Contribution

It introduces the impact of direct exchange interactions on phase transitions and critical phenomena in the Kondo lattice model, including new magnetic phases and universal critical exponents.

Findings

Identifies a continuous quantum phase transition to the Kondo singlet state.

Finds a universal critical exponent for magnetization curves.

Explains the local minimum of the Kondo temperature observed experimentally.

Abstract

We study the Kondo lattice model with a direct antiferromagnetic exchange interaction between localized moments. Ferromagnetically long-range ordered state coexisting with the Kondo screening shows a continuous quantum phase transition to the Kondo singlet state. We obtain the value of the critical point where the magnetizations of the localized moments and the conduction electrons vanish. The magnetization curves yield a universal critical exponent independent of the filling factors and the strength of the interaction between localized moments. It is shown that the direct exchange interaction between localized moments introduces another phase transition from an antiferromagnetic ordering to a ferromagnetic ordering for small Kondo exchange interaction. We also explain the local minimum of the Kondo temperature in recent experiments.