Muon Spin Rotation and Relaxation in the Superconducting Ferromagnet UCoGe

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 ${T}_{C}=3\text{ }\text{ }\mathrm{K}$. The ${\ensuremath{\mu}}^{+}$ precession frequency persists below the bulk superconducting transition temperature ${T}_{\mathrm{sc}}=0.5\text{ }\text{ }\mathrm{K}$, where it measures a local magnetic field ${B}_{\mathrm{loc}}=0.015\text{ }\text{ }\mathrm{T}$. The amplitude of the $\ensuremath{\mu}\mathrm{SR}$ signal provides unambiguous proof for ferromagnetism present in the whole sample volume. We conclude ferromagnetism coexists with superconductivity on the microscopic scale.