NEUTRON-DIFFRACTION STUDY OF MAGNETIC ORDERING IN UP0.75S0.25

The magnetic ordering of UP0.75S0.25, which has the NaCl-type structure, has been determined by powder neutron-diffraction techniques. The initial ordering at about 100°K is ferromagnetic. At around 70°K, a ferrimagnetic structure appears in which ferromagnetic (001) sheets are directed along the c axis in the sequence 5+, 4-, 5+, 4-,.... This corresponds to a ferrimagnetic antiphase type of structure in which the period of modulation is 4.5c and which closely resembles the low-temperature structure of thulium. The ordered moment in this structure is about 1.4μB per uranium atom, and the net spontaneous moment is 0.16μB, which is in agreement with magnetization measurements. Below about 20°K, a further transition occurs, resulting in the type-IA antiferromagnetic structure, in which the sheets are stacked in the sequence 2+, 2-, 2+, 2-,... with an ordered moment of 1.7±0.05μB. The magnetic ordering in this material, which is a good conductor of electricity, provides strong evidence that long-range oscillatory interactions of Ruderman-Kittel-Kasuya-Yosida (RKKY) type between localized moments are important in actinide materials. © 1969 The American Physical Society.