One dimensional antiferromagnetism in K2FeF5: a single crystal Mossbauer study

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Abstract
Mossbauer spectra of K2FeF5 obtained in a magnetic field applied parallel to the antiferromagnetic axis show that in a field of 3.7T the spins reorientate (flop) to become perpendicular to the applied field. The experimental value of the spin-flop field yields an approximate value of 1.4*10-3 for the ratio BA/BE of the anisotropy field to the exchange field. The applied field spectra also show a dependence of the hyperfine field on the applied field. This behaviour together with the anomalously low value of the saturation hyperfine field (41.0+or-0.5 T) and the temperature dependence of the hyperfine field are discussed in terms of the spin reduction, which results from a spin-wave treatment of an antiferromagnet. Calculations show that this spin reduction is enhanced in a one dimensional system. Comparison of the calculated and experimental values leads to an estimate of around 10-3 for the ratio J'/J of the interchain to the intrachain exchange constants, which shows that K2FeF5 provides a good approximation to a one dimensional magnetic system.