Metamagnetism and tricriticalilty in heavy-fermion ferromagnet URhGe

TL;DR

This paper develops a theoretical model to explain the magnetic phase transitions and tricritical behavior in the heavy-fermion ferromagnet URhGe, revealing a tricritical point and mean-field critical exponents.

Contribution

It introduces a spin model with competing anisotropies to describe URhGe's magnetic phase diagram, including a tricritical point and critical behavior analysis.

Findings

Identification of a tricritical point in the phase diagram.

Mean-field critical exponents describe the tricritical behavior.

Analytical and Monte Carlo methods confirm the phase transition features.

Abstract

URhGe is a ferromagnetic superconductor with a distinctive magnetic behavior. In a field applied parallel to the b-axis and perpendicular to the easy axis, URhGe exhibits an abrupt orientational transition of the magnetization with a reentrant superconducting phase emerging close to the transition field. We develop a theoretical description of the magnetic properties of URhGe by considering a spin model with competing magnetic anisotropies. The model is analyzed both analytically at zero temperature and with Monte Carlo simulations at finite temperatures. The constructed H-T phase diagram for a magnetic field parallel to the b-axis features a tricritical point on the line of phase transitions between the ferromagnetic Ising state and the paramagnetic phase. We also demonstrate that the asymptotic tricritical behavior of the order parameter and the correlation length is described by the mean-field critical exponents.