Thermal expansion of the superconducting ferromagnet UCoGe

TL;DR

This study investigates the anisotropic thermal expansion of UCoGe, a superconducting ferromagnet, revealing bulk phase transitions and a possible change in the magnetic transition's nature under magnetic fields.

Contribution

First detailed measurement of anisotropic thermal expansion in UCoGe, linking thermal anomalies to bulk magnetism and superconductivity, and exploring magnetic field effects.

Findings

Pronounced anisotropy in thermal expansion along crystal axes.

Large step sizes at phase transitions confirm bulk properties.

Magnetic field enhances the ferromagnetic transition's first-order character.

Abstract

We report measurements of the coefficient of linear thermal expansion, $\alpha (T)$, of the superconducting ferromagnet UCoGe. The data taken on a single-crystalline sample along the orthorhombic crystal axes reveal a pronounced anisotropy, with the largest length changes along the $b$ axis. The large values of the step sizes $\Delta \alpha$ at the magnetic and superconducting phase transitions provide solid evidence for bulk magnetism and superconductivity. Specific-heat measurements corroborate bulk superconductivity. Thermal-expansion measurements in magnetic fields $B \parallel a,b$ show $\Delta \alpha$ at $T_C$ grows rapidly, which indicates the character of the ferromagnetic transition becomes first-order-like.