STRUCTURAL AND MAGNETIC CHARACTERIZATION OF A NEW PHASE OF CRCL2

A new structural phase of the quasi-one-dimensional antiferromagnet Cr Cl2 could be prepared by Bridgman technique. The new phase differs fro m the known crystal structure by doubling of the lattice constant alon g the b axis, and is isostructural to HgCl2. The structural refinement of neutron diffraction data reveals strong substitutional disorder, w hich can be regarded as stacking disorder of Cl layers. The disorder g ives rise to a coexistence of two structural phases in the investigate d samples. The magnetic moments of each phase order at different tempe ratures T-N1 = 16.0 K and T-N2 = 11.3K, respectively. Powdering of the crystals destroys the new phase, and the powder diffractogram display s only the pattern of the known CrCl2 structure. Above the Neel temper ature, incommensurate short-range order occurs due to magnetic frustra tion effects between spins of adjacent chains. The ratio between inter chain and intrachain coupling could be estimated from the incommensura te position of the diffuse scattering to be J'(1)/J approximate to 0.1 3. (C) 1997 Elsevier Science Ltd.