UMBRELLA AND FAN PHASE DETECTED IN CSNI0.98FE0.02CL3

The substitution of a few percent of Fe2+ for Ni2+ in the stacked-tria ngular antiferromagnet CsNi0.98Fe0.02Cl3 leads to a compensation of th e weak Ising anisotropy of the pure compound and induces an XY anisotr opy in the doped system. Neutron diffraction experiments have been per formed in order to determine the magnetic phase diagram and magnetic s tructures in applied fields H perpendicular to c up to 5 T between T = 1.8 and 6 K. The phase diagram and spin configurations are discussed with respect to theoretical predictions. (C) 1998 Elsevier Science B.V . All rights reserved.