We present inelastic neutron scattering measurements and first principles calculations examining the intermetallic marcasite CrSb2. The observed spin wave dispersion implies that the magnetic interactions are strongly one-dimensional with antiferromagnetic chains parallel to the crystalline c-axis. Such low-dimensional excitations are unexpected in a semiconducting intermetallic system. Moreover this material may be further interesting in that the magnetic anisotropy may enhance thermoelectric properties along particular crystallographic directions. [3] have found changes in the electronic properties, with an increase in the thermoelectric figure of merit for Te substitution. CrSb 2 has also been considered as an electrode material for lithium based batteries showing improvement compared to using pure antimony.[4, 5] Here we report inelastic neutron scattering (INS) measurements and first principles calculations for this compound. We find that CrSb 2 has significant exchange anisotropy exhibiting a quasi-onedimensional (1d) magnon spectrum. This spectrum has implications for the thermal conductivity as a function of crystallographic direction. In addition, the determined exchange constants and anisotropy allow one to classify CrSb 2 as an S = 1 antiferromagnetic (AFM) chain with interchain coupling and on-site anisotropy.CrSb 2 is an intermetallic marcasite where the Cr atoms are located at the body center and corner positions of the orthorhombic unit cell with room temperature lattice constants a = 6.028, b = 6.874, and c = 3.272Å.[6] The Cr atoms are at the center of a distorted octahedron of Sb sites as shown in Fig. 1. Early thermodynamic measurements found CrSb 2 to have AFM correlations [8,9], but the ordered magnetic phase with T N = 273(2) K was not observed until much later.[7] The ordered magnetic structure is shown in Fig. 1 Local spin density approximation (LSDA) calculations were performed using the general potential linearized augmented planewave (LAPW) method.[11] Local orbital extensions were employed to include the high lying semicore states and to relax any linearization errors. The calculations included no shape approximations to either the potential or charge density. Relativity was included for the valence states within a scalar relativistic approximation, while full relativity was included for the core states, within an atomic like approximation. Well converged basis sets consisting of more than 850 LAPW functions plus local orbitals were used for the primitive unit cell (two formula units) of CrSb 2 . Brillouin zone samplings were done with the special k-points method, using 128

A study of the quasi-twodimensional antiferronmget KFeF4 below the a s i t i o n temperature. TN = 13 K, has been undemken using neutron scattering techniques. The dispersion relation of the spin excitations is well described by a model Hamiltonian incorporating Heisenberg exchange interactions and uniaxial anisotropy. The anisotropy controls the energy of the zone centre mode whose frequency varies in the same way with temperature as the square of the staggered magnetization which is described by the two-dimensional king model. Dipoledipolecontributions are too small to account fnlly for the anisotropy. Different nearest-neighbour exchange enersies are found along the a and b directions due to different superexchange paths, with Jl = -2.18 meV along a, and Jz = -2.73 meV along b.

The spin-wave excitations of the near-ideal 3D Heisenberg antiferromagnet RbMnF3 have been measured in the presence of an applied fled using neutron scattering. Detailed measurements of both the wave vector and field dependence of the excitations were made for fields up to 5.7 T. For applied fields >or=0.26 T, the spins undergo a spin-flop transition. In this phase the twofold degeneracy of the zero-field spin waves is lifted. A rigorous analysis of the data, allowing for the effects of instrumental resolution, shows that the excitations are well explained by linear spin-wave theory. No evidence is found for higher-order processes, such as have been found in systems of lower dimensionality.