Magnetic phase diagram of USb at high pressure

High-pressure resistance and neutron scattering measurements have been performed on single crystals of USb. It is shown that the effect of pressure is to reduce the ordering temperature of the antiferromagnetic triple- k phase at a rate of -17 K/GPa. This phase exists at least up to 6 GPa. However, above 2 GPa, a second magnetic phase transition occurs at low temperature, below about 80 K. From the neutron data, the new phase is found to have the same wave vector, k = (1,0,0), as the triple- k structure, but a careful analysis of domain population effects suggests that it is most likely single- k . The appearance of a single- k structure at low temperature, while a multi- k structure is stable at a higher temperature, is at variance with the behaviour normally encountered in this type of systems. However, it is shown to fit into a unified phase diagram of the uranium monopnictides.