Wing structure in the phase diagram of the Ising Ferromagnet URhGe close to its tricritical point investigated by angle-resolved magnetization measurements

TL;DR

This study maps the wing structure of the phase diagram in URhGe near its tricritical point using angle-resolved magnetization measurements, revealing detailed transition behaviors and critical points.

Contribution

The paper provides the first detailed experimental mapping of the wing structure in URhGe's phase diagram near the tricritical point, including the detection of first-order transitions and critical points.

Findings

Detection of first-order transition at low temperatures

Identification of quantum wing critical points at specific magnetic fields

Evidence of a tricritical point above 4 K

Abstract

High-precision angle-resolved dc magnetization and magnetic torque studies were performed on a single-crystalline sample of URhGe, an orthorhombic Ising ferromagnet with the $c$ axis being the magnetization easy axis, in order to investigate the phase diagram around the ferromagnetic (FM) reorientation transition in a magnetic field near the $b$ axis. We have clearly detected first-order transition in both the magnetization and the magnetic torque at low temperatures, and determined detailed profiles of the wing structure of the three-dimensional $T$-$H_{b}$-$H_{c}$ phase diagram, where $H_{c}$ and $H_{b}$ denotes the field components along the $c$ and the $b$ axes, respectively. The quantum wing critical points are located at $\mu_0H_c\sim\pm$1.1 T and $\mu_0H_b\sim$13.5 T. Two second-order transition lines at the boundaries of the wing planes rapidly tend to approach with each other with increasing temperature up to $\sim 3$ K. Just at the zero conjugate field ($H_c=0$), however, a signature of the first-order transition can still be seen in the field derivative of the magnetization at $\sim 4$ K, indicating that the tricritical point exists in a rather high temperature region above 4 K. This feature of the wing plane structure is consistent with the theoretical expectation that three second-order transition lines merge tangentially at the triciritical point.