A Mossbauer investigation of Rb2FeF5: A one-dimensional antiferromagnetic system

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Abstract
Mossbauer spectra of Rb2FeF5show that it undergoes an ordering to a four sublattice antiferromagnetic state at 9.3+or-0.5K. The saturated value of the hyperfine field is 43.0+or-0.5 T, and is the same for both pairs of sublattices. This value is anomalously low for a high-spin ferric ion and corresponds to a zero-point spin reduction of about 28%. At finite temperatures the hyperfine fields at the iron nuclei are appreciably modified by the application of an external magnetic field. This behaviour is a characteristic of one-dimensional antiferromagnets. Relationships for the spin reduction as a function of the magnitude and direction of the external field are developed on the basis of spin wave theory. The measured values of the hyperfine fields are compared with those calculated from these relationships which leads to the ratio J'/J of the intrachain to interchain exchange constants being less than 10-3and the ratio BA/BEof anisotropy to exchange fields being around 4*10-3.