Neutron diffraction study of UAssub(0.95)Sesub(0.05) single crystal disappearance of the type-1 antiferromagnetic structure

A single crystal of UAssub(0.95)Sesub(0.05) has been studied by neutron diffraction. It orders at Tsub(N)=121.5 K with an incommensurate phase, characterized by a wavevector k=[00k] with k(Tsub(N)-0.619). On lowering the temperature, two different magnetic behaviours are observed. First an incommensurate-commensurate transition at Tsub(IC)=106 K to the type-I antiferromagnetic phase (+-+-), with k(Tsub(IC))=0.596, is followed by a transition at T0=93 K to the type-IA antiferromagnetic phase (++--). The second one corresponds to an incommensurate phase which transforms directly to type-IA at Tsub(IC)=103 K. These behaviours determine the critical composition, chiapprox.=0.05, for the disappearance of the type-I structure in the arsenic-rich UAssub(1-x)Sesub(x) solid solutions. The magnetic phase diagram in this region is established and compared with previous versions. (orig.)