MAGNETIC PHASE-DIAGRAM OF THE U(RH1-XRUX)SI2 SYSTEM

The magnetic phase diagram of the solid solutions U(Rh1-xRux)2Si2 has been studied by resistivity and susceptibility measurements and neutron diffraction on powder and single crystals. In the range 0 < x < 0.6 an antiferromagnetic structure (k = [001], m parallel-to c) is observed. The Neel temperature first increases from T(N) = 137 K (x = 0) upto T(N) = 174 K (x = 0.375) and then decreases down to T(N) = 101 K (x = 0.6). The ordered U magnetic moment keeps a constant value of about 2-mu(B)/U. In between x = 0.6 and x = 0.65 the Neel temperature jumps from 101 K (x = 0.6) to 44 K (x = 0.65) and the magnetic ordering changes towards a commensurate structure of wave vector [1/2 1/2 1/2]. For larger x, the ordering temperature and the ordered moment decrease and vanish at about x = 0.92. Above this concentration only short-range magnetic correlations centered around [1/2 1/2 1/2] are observed before they reach the peculiar behaviour of URu2Si2.