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From the knowledge of the spin correlation functions derived from Mössbauer relaxation spectra of quasi-one-dimensional A 2 MnoyxFe ()() 2F< i (H20) we could fit the antiferromagnetic susceptibilities of A 2 MnF 5 (H 2 0) with A = Na , (NH 4 ) + , K + , Rb + obtained for single crystal samples. The calculation yielded characteristic parameters such as the local anisotropy D, the intra-chain exchange energy J, the inter-chain exchange energy \ J'\, the Neel temperature T N , and the spin canting angle (p.

Measurements of the

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Electron-spin-resonance (ESR) experiments have been performed on the quasione-dimensional magnet (NH 4 ) 2 MnF 5 . The ESR spectrum consists of two components, an extremely broad signal and a weak but sharp resonance on top of the broad signal. The resonance field of the dominating broad signal is most probably shifted by strong non-diagonal terms of the dynamic susceptibility to g-values well below g = 2 and becomes undetectable upon the onset of strong one-dimensional correlations below T 60 K. We attribute these two signals to Mn 3+ ions of the chains (broad resonance, intrinsic response of the sample) and to defects (small resonance), respectively. The ESR spectra reflect the evolution from the paramagnetic state (T > 60 K) to one-dimensional magnetic behaviour (T 60 K). The results are discussed with respect to the local anisotropy of the Mn 3+ ions and comparison is made with the behaviour of other one-dimensional magnetic compounds.