Tricritical point and wing structure in the itinerant ferromagnet UGe2

TL;DR

This study identifies the tricritical point and wing structure in the phase diagram of the itinerant ferromagnet UGe2 through resistivity measurements under pressure and magnetic field, revealing new insights into its phase transitions.

Contribution

It is the first to locate the tricritical point and boundary of the first order transition plane in the p-T-H phase diagram of UGe2, a weak itinerant ferromagnet.

Findings

Identification of the tricritical point in UGe2

Observation of the first order transition boundary in the phase diagram

Estimation of the quantum critical point location

Abstract

Precise resistivity measurements on the ferromagnetic superconductor UGe2 under pressure p and magnetic field H reveal a previously unobserved change of the anomaly at the Curie temperature. Therefore, the tricritical point (TCP) where the paramagnetic-to-ferromagnetic transition changes from a second order to a first order transition is located in the p-T phase diagram. Moreover, the evolution of the TCP can be followed under the magnetic field in the same way. It is the first report of the boundary of the first order plane which appears in the p-T-H phase diagram of weak itinerant ferromagnets. This line of critical points starts from the TCP and will terminate at a quantum critical point. These measurements provide the first estimation of the location of the quantum critical point in the p-H plane and will inspire similar studies of the other weak itinerant ferromagnets.