Muon spin rotation and relaxation in the superconducting ferromagnet UCoGe

TL;DR

This study uses muon spin rotation and relaxation techniques to demonstrate that ferromagnetism and superconductivity coexist microscopically in UCoGe, with ferromagnetic order persisting below the superconducting transition.

Contribution

First direct evidence of microscopic coexistence of ferromagnetism and superconductivity in UCoGe using muon spin rotation measurements.

Findings

Ferromagnetic order detected below 3 K.

Superconductivity persists below 0.5 K.

Ferromagnetism is present throughout the entire sample volume.

Abstract

We report zero-field muon spin rotation and relaxation measurements on the superconducting ferromagnet UCoGe. Weak itinerant ferromagnetic order is detected by a spontaneous muon spin precession frequency below the Curie temperature $T_C = 3$ K. The $\mu^+$ precession frequency persists below the bulk superconducting transition temperature $T_{sc} = 0.5$ K, where it measures a local magnetic field $B_{loc} = 0.015$ T. The amplitude of the $\mu$SR signal provides unambiguous proof for ferromagnetism present in the whole sample volume. We conclude ferromagnetism coexists with superconductivity on the microscopic scale.