Abstract
Inelastic neutron scattering has been used to study the magnetic excitation spectrum of KFeS 2 –a spin analogue of the oxidized two iron ferredoxins–in the antiferromagnetically ordered state. The observed spin wave dispersion relations along a * , b * , c * directions at 77 K are analyzed to give the nearest neighbor intra-chain exchange constant J 1 =-168.1±4.8 cm -1 (-20.84±0.60 meV), and the ratio of the nearest interchain to the intra-chain interaction | J 3 |/| J 1 |=8.6×10 -3 indicative of the strong covalency and of the one-dimensional character of the interaction. The anisotropy field of 6040±91 Oe obtained from the gap at the zone center results mostly from the non-dipolar energy. A contribution of quartic terms of spins in the anisotropy energy is needed to account for the observed easy spin direction.
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