Collapse of 5f-electron ferromagnetism in UPtAl under high pressures

UPtAl exhibits a ferromagnetic ordering of U magnetic moments at temperatures below T_C = 42.5 K. The magnetic-ordering transition is accompanied by an anomaly in the temperature dependence of electrical resistivity. This allows us to determine the value of Curie temperature from p vs. T data that can be measured at very high pressures, at which reliable magnetization measurements are difficult. We report on resistivity measurements performed on an UPtAl single crystal under hydrostatic pressures p ≤ 8 GPa. It was observed that the initial increase of T_C with p becomes gradually reduced for p > 2 GPa until the maximum T_C value of ≈48 K is reached between 4 and 6 GPa that is followed by a progressively developing downturn of the T_C(p) curve. The latter result is attributed to the approaching collapse of the U 5f-moment ferromagnetism. Low-temperature resistivity data point to a rapidly reduced magnetic anisotropy at highest pressures.