Spin ordering in a triangular X-Y antiferromagnet: CsFeCl3 and RbFeCl3

Spin ordering and its possible frustration in an antiferromagnetic system of X-Y spins with a triangular network are studied by measuring susceptibility and specific heat of CaFeCl3 and RbFeCl3 single crystals at 1.0 approx. equal to 4.2 K up to 14 T. The T-H phase diagrams are obtained. By the specific heat measurement under the field along the c-axis, we found for the first time there appear one or two rather broad humps followed by a sharp peak with decreasing temperatures for both salts. It suggests presumably the successive transitions into the rigidly ordered phase. The results are discussed in comparison with the phase diagrams predicted for some triangular antiferromagnetic systems. (orig.)