Neutron diffraction measurements were carried out on single crystals of CsCoCl 3 , a quasi-one-dimensional antiferromagnet of Ising-like spins, in the long range ordered region. The determined magnetic structure at 4.2 K is composed of antiferromagnetic stacking of ferrimagnetic c -plane with three sublattices as determined by Melamud et al. The spins are aligned along c -axis and were evaluated to be 3.11 µ B at 0 K by extrapolation. Unusual temperature dependence of magnetic reflection intensity was observed and interpreted as a partial disordering transition in which one of the three sublattices in a c -plane loses its magnetization above 13.5 K resulting in antiferromagnetic c -planes. This transition is discussed in connection with the antiferro-ferrimagnetic transition in the triangular Ising lattice. The critical exponent of the magnetization was found to be 0.34 around the Neel temperature 20.82 K.

Magnetic Structure of CsCoCl 3

Successive phase transitions of triangular lattice Heisenberg antiferromagnet with a small Ising anisotropy, CsNiCl 3 , are studied by neutron scattering We have reexamined the temperature dependences of the z and x y components of sublattice magnetizations and also measured the both components of staggered susceptibilities The character of the transitions is orderings and divergences of the z and x y components at independent temperatures

Neutron Scattering Study of Successive Phase Transitions in Triangular Lattice Antiferromagnet CsNiCl3

The authors report inelastic polarized neutron scattering measurements of the excitations in the S=1, quasi-one-dimensional antiferromagnet CsNiCl3 with applied magnetic field. A field up to 5.9 T was applied perpendicular to the chain direction and the field dependence of spin excitation modes at wave vectors corresponding to the one-dimensional zone centre (i.e. ( xi , xi ,1)) was studied. Near the antiferromagnetic ordering point Q=(1/3,1/3,1) two types of field dependence are observed. The behaviour of the higher energy mode suggests that it is the novel longitudinal mode recently proposed by Affleck (1989). The application of the field also reveals a near-degeneracy of the excitations observed at Q=(0,0,1) in zero field. This degeneracy is incompatible with the result of the classical spin wave theory based on the Heisenberg Hamiltonian with a single-site anisotropy.

Inelastic polarized neutron scattering from S=1 antiferromagnetic CsNiCl3 in an applied field

We study ESR modes in the ground states of hexagonal ABX 3 -type antiferromagnets with easy-axis anisotropy such as CsNiCl 3 , RbNiCl 3 , CsMnI 3 . Taking a six sublattice model for the spin structure, we investigate the normal modes for the motions of the sublattice magnetizations within the framework of mean field approximation. In general, six kinds of modes are obtained by solving the classical equation of motion, d M i /d t =[ M i × H i ]. Frequency field diagram is presented. Ground state properties of fields for resonance and line widths of ESR spectra on CsNiCl 3 , RbNiCl 3 and CsMnI 3 are reported. Calculated values of resonance fields are in agreement with experimental results. The weak interchain exchange interaction constant J 1 is estimated with good accuracy as J 1 / k B =-2.8×10 -2 K for CsNiCl 3 and -7.5×10 -2 K for CsMnI 3 .

A. Sorgen

Papers

Spin waves in the nearly one-dimensional systems of CsNi Cl 3 and RbNi Cl 3