Pressure-phase diagram of UCoGe by ac-susceptibility and resistivity measurements

TL;DR

This study maps the pressure-temperature phase diagram of UCoGe, revealing that superconductivity persists beyond the suppression of ferromagnetism, indicating a unique coexistence and extension of superconductivity into the paramagnetic phase.

Contribution

First detailed pressure-phase diagram of UCoGe using simultaneous resistivity and ac-susceptibility measurements, showing superconductivity extends beyond ferromagnetic suppression.

Findings

Ferromagnetic phase suppressed near 1.2 GPa

Superconductivity persists up to at least 2.4 GPa

UCoGe is the first known compound where superconductivity extends into the paramagnetic region

Abstract

UCoGe is one of the few compounds showing the coexistence of ferromagnetism and superconductivity at ambient pressure. With T_Curie = 3 K and T_SC = 0.6 K it is near a quantum phase transition; the pressure needed to suppress the magnetism is slightly higher than 1 GPa. We report simultaneous resistivity and ac-susceptibility measurements under pressure on a polycrystal with very large single-crystalline domains and a resistivity ratio of about 6. Both methods confirm the phase diagram established before by resistivity measurements on a polycrystal. The ferromagnetic phase is suppressed for P approximately 1.2 GPa. Astonishingly, the superconductivity persists at pressures up to at least 2.4 GPa. In other superconducting and ferromagnetic heavy fermion compounds like UGe2 and URhGe, the superconducting state is situated only inside the larger ferromagnetic region. Therefore, UCoGe seems to be the first example where superconductivity extends from the ferromagnetic to the paramagnetic region.