High-pressure susceptibility studies on the ferromagnetic uranium monochalcogenides US, USe and UTe

The dependence of the Curie temperature T-c of the ferromagnetic compounds UX (X = S, Se or Te) on hydrostatic pressure to 13 GPa has been determined using a diamond-anvil cell loaded with dense helium as pressure medium. A sensitive primary/secondary coil system allows the detection of the ferromagnetic transition in the ac susceptibility for tiny samples with mass less than or equal to 1 mu g. The Curie temperatures of USe (170 K) and UTe (102 K) initially increase with applied pressure at the rates + 2.7 K/GPa and + 13.3 K/GPa, passing through maxima at pressures of approximately 6 GPa and 7 GPa, respectively. T-c for US (173 K) decreases monotonically under pressure at the rate -3.9 K/GPa. For all three chalcogenides the pressure dependence of T-c is clearly influenced by structural phase transitions. The present results are compared to those from earlier resistivity studies and discussed within the framework of both a phase diagram proposed by Doniach for local-moment Kondo-lattice systems and pressure-dependent itinerant electron magnetism.