Ferromagnetic phases in spin-Fermion systems

TL;DR

This paper develops a renormalized spin-wave theory to describe ferromagnetic phases in spin-Fermion systems, explaining temperature-dependent magnetization and interpreting experimental data for UGe2.

Contribution

It introduces an extended renormalized spin-wave theory accounting for magnon interactions to analyze two distinct ferromagnetic phases in spin-Fermion systems.

Findings

Describes two ferromagnetic phases with different electron contributions.

Calculates magnetization as a function of temperature.

Provides theoretical interpretation of experimental magnetization curves for UGe2.

Abstract

Spin-Fermion systems which obtain their magnetic properties from a system of localized magnetic moments being coupled to conducting electrons are considered. The dynamical degrees of freedom are spin-$s$ operators of localized spins and spin-1/2 Fermi operators of itinerant electrons. Renormalized spin-wave theory, which accounts for the magnon-magnon interaction, and its extension are developed to describe the two ferrimagnetic phases in the system: low temperature phase $0<T<T^{*}$, where all electrons contribute the ordered ferromagnetic moment, and high temperature phase $T^{*}<T<T_C$, where only localized spins form magnetic moment. The magnetization as a function of temperature is calculated. The theoretical predictions are utilize to interpret the experimentally measured magnetization-temperature curves of $UGe_2$..