Anomalous spin distribution in the superconducting ferromagnet UCoGe studied by polarized neutron diffraction

TL;DR

This study uses polarized neutron diffraction to investigate the weak ferromagnetic moments in superconducting UCoGe, revealing unusual Co atom polarization and its potential link to quantum criticality.

Contribution

It provides the first detailed analysis of the anomalous spin distribution in UCoGe, highlighting the induced Co moment and its implications for understanding ferromagnetic superconductivity.

Findings

U atom carries the primary magnetic moment in the normal phase.

Increasing magnetic field enhances the U moment and induces a significant antiparallel Co moment.

The Co 3d orbitals exhibit unique polarizability, suggesting proximity to a quantum critical point.

Abstract

We report a polarized neutron diffraction study conducted to reveal the nature of the weak ferromagnetic moment in the superconducting ferromagnet UCoGe. We find that the ordered moment in the normal phase in low magnetic fields (B // c) is predominantly located at the U atom and has a magnitude of about 0.1 muB at 3 T, in agreement with bulk magnetization data. By increasing the magnetic field the U moment grows to about 0.3 muB in 12 T and most remarkably, induces a substantial moment (about 0.2 muB) on the Co atom directed antiparallel to the U moment. The anomalous polarizability of the Co 3d orbitals is unique among uranium intermetallics and might reflect the proximity to a magnetic quantum critical point of UCoGe in zero field.