MAGNETIC-ORDERING IN URANIUM MONOPHOSPHIDE

The magnetic ordering in uranium monophosphide (UP) has been studied by neutron diffraction from a single crystal in a magnetic field. UP orders at T//N congruent 122 plus or minus 0. 1 K with the type-I antiferromagnetic structure, the ordering taking place in a first-order transition. At T//0 equals 22. 5 K the ordered magnetic moment jumps from 1. 7 mu //B to 1. 9 mu //B. With a magnetic field H equals 25 kOe applied in the appropriate direction, it is found that UP has the collinear single-k type-I structure above T//0 and undergoes a first-order transition to the planar double-k type-I structure, accompanied by a 'moment jump' due to the change in the moment direction from LT AN BR 001 RT AN BR to LT AN BR 110 RT AN BR .