Muon spin rotation in the molecular-based layer ferrimagnets AFe(II)Fe(III)(C2O4)(3) (A = N(n-C4H9)(4), P(C6H5)(4))

Zero field muon spin rotation was measured in polycrystalline samples of tw o molecular-based layer ferrimagnets AFe(II)Fe(II)(C2O4)(3) with A = N(n-C4 H9)(4) and P(C6H5)(4) which, although having the same honeycomb layer struc ture, show, respectively, negative and positive low field magnetisation at low temperature. The time dependence of the muon decay asymmetry, measured between 100 and 4.5 K, is modelled best by a combination of fast Gaussian a nd slow Lorentzian functions. Sharp falls in the asymmetry at 44 K (N(n-C4H 9)(4)) and 38 K (P(C6H5)(4)) are identified with the transition to long-ran ge magnetic order. (C) 1999 Published by Elsevier Science Ltd. All rights r eserved.