Magnetic features of the (U0.50Tm0.50)Ni2B2C solid solution

The quaternary borocarbides TmNi2B2C and UNi2B2C crystallize in the body-ce ntered tetragonal LuNi2B2C-type structure, and exhibit antiferromagnetic or der below 1.53 and 218 K, respectively. The magnetic structure of TmNi2B2C is characterized by incommensurate, long-range, spin-density-wave in the ba sal plane, with Tm moments along the c-axis, and does not involve ferromagn etic basal planes, while that of UNi2B2C is assumed to contain U moments al ong the c-axis in ferromagnetic basal planes. In the system (U,Tm)Ni2B2C th e different magnetic structures of the end compounds result in a frustratio n of magnetic moments, which is not just directional. Indeed, the newly-pre pared intermediate solid solution (U0.50Tm0.50)Ni2B2C is paramagnetic down to 2 K, for both as-cast and annealed samples, with no indication for any c ooperative phenomenon. The paramagnetic values of the annealed sample [thet a = -5.6(5) K, mu (eff) = 5.4(1) muB] are compatible with those of the end compounds. (C) 2001 Elsevier Science B.V. All rights reserved.