Effect of Organic Cation A on the Crystal Structure and Magnetisation of the Layer Molecular Ferrimagnets AFeIIFeIII(C2O4)3

Abstract

We survey the crystal and magnetic structures and bulk magnetisation for representative examples of the series of ferrimagnetic tris-oxalato-ferrate(II,III) salts with general formula AFeII FeII(C2O4)3 (A = quaternary ammonium, phosphonium). The compounds all crystallise in two-dimensional hexagonal honeycomb lattices but while some show positive magnetisation at low temperature (Néel type Q) others show a large negative magnetisation below a compensation temperature Tcomp (Néel type N). In compounds that exhibit negative magnetisation a discontinuity in the magnetisation is observed at Tt (Tcomp < Tt < Tc) indicative of a magneto-strictive transition. In compounds that exhibit positive magnetisation, hysteresis and frequency dependent AC susceptibility indicate a glassy magnetic order at low temperatures, possibly arising from the frustration of random anisotropy domains below a blocking temperature, or imbalance and disorder of Fe(II) and Fe(III).