Two Ferromagnetic Phases in Spin-Fermion Systems

TL;DR

This paper investigates spin-fermion systems with localized spins and itinerant electrons, revealing two distinct ferromagnetic phases and identifying a characteristic temperature where electron magnetization vanishes, aligning with experimental data.

Contribution

It introduces a modified spin-wave theory showing the existence of two ferromagnetic phases in spin-fermion systems, including a novel high-temperature phase with only localized spin contribution.

Findings

Identification of two ferromagnetic phases

Magnetization of itinerant electrons drops to zero at T*

Agreement with experimental data on UGe2

Abstract

We consider spin-fermion systems which get their magnetic properties from a system of localized magnetic moments being coupled to conducting electrons. The dynamical degrees of freedom are spin-$s$ operators of localized spins and spin-1/2 fermi operators of itinerant electrons. We develop modified spin-wave theory and obtain that system has two ferromagnetic phases. At the characteristic temperature T* the magnetization of itinerant electrons becomes zero, and high temperature ferromagnetic phase (T*<T<T_C) is a phase where only localized electrons give contribution to the magnetization of the system. An anomalous increasing of magnetization below T* is obtained in a good agrement with experimental measurements of the ferromagnetic phase of UGe2.