Relationship between Ferromagnetic Criticality and the Enhancement of Superconductivity Induced by Transverse Magnetic Fields in UCoGe

TL;DR

This study investigates how transverse magnetic fields influence ferromagnetic criticality and superconductivity in UCoGe, revealing that magnetic anisotropy and criticality are key to superconductivity enhancement.

Contribution

It demonstrates that magnetic field orientation induces ferromagnetic criticality, which correlates with superconductivity enhancement in UCoGe, a novel insight into magnetic-superconducting interplay.

Findings

Ferromagnetic criticality is induced only when H is along the b axis.

Superconductivity is enhanced in H || b above 5 T.

Magnetic anisotropy influences the relationship between ferromagnetism and superconductivity.

Abstract

We have performed 59Co NMR experiments on the ferromagnetic superconductor UCoGe under magnetic fields (H) along the a- and b- axes to investigate the relationship between ferromagnetic properties and superconductivity. The ferromagnetic ordering temperature TCurie is suppressed and the nuclear spin-lattice relaxation rate 1/T1 at 2 K is enhanced in H || b, although TCurie and 1/T1 are unchanged in H || a, indicating that the ferromagnetic criticality is induced only when H is applied along the b axis. We show the close relationship between the magnetic anisotropies and the superconducting ones reported by Aoki et al.: the superconductivity is gradually suppressed in H || a, but enhanced in H || b above 5 T. We strongly suggest that the enhancement of the superconductivity observed in H || b originates from the field induced ferromagnetic criticality, as pointed out by Aoki et al and Mineev.