Pressure-induced quantum phase transition in the itinerant ferromagnet UCoGa

TL;DR

This study investigates the pressure-induced quantum phase transition in UCoGa, revealing a first-order transition from ferromagnetic to paramagnetic state around 6.5 GPa and mapping the phase diagram features.

Contribution

It provides the first detailed high-pressure measurements of UCoGa, identifying the quantum critical point and characterizing the phase transition nature.

Findings

Ferromagnetic order disappears at ~6.5 GPa

Magnetic moment decreases with pressure up to 6 GPa

Phase diagram features a tricritical point at ~6 GPa and 30 K

Abstract

In this paper, we report the results of a high pressure study of the itinerant 5f-electron ferromagnet UCoGa. The work is focused on probing the expected ferromagnet-to-paramagnet quantum phase transition induced by high pressure and on the general features of the P-T(-H) phase diagram. Diamond anvil cells were employed to measure the magnetization and electrical resistivity under pressures up to ~ 10 GPa.At ambient pressure, UCoGa exhibits collinear ferromagnetic ordering of uranium magnetic moments {\mu}U ~ 0.74 {\mu}B (at 2 K) aligned along the c-axis of the hexagonal crystal structure below Curie temperature TC = 48K. With the application of pressure, gradual decrease of both, TC and the saturated magnetic moment, has been observed up to pressures ~ 6 GPa. This is followed by a sharp drop of magnetic moment and a sudden disappearance of the magnetic order at the pressure of 6.5 GPa, suggesting a first-order phase transition, as expected for a clean system. The low temperature power law dependence of the electrical resistivity shows distinct anomalies around the ~ 6 GPa, consistent with the pressure evolution of the magnetic moment and the ordering temperature. The tricritical point of the UCoGa phase diagram is located at approximately ~ 30 K and ~ 6 GPa.