Magnetization of the layer compounds AFeIIFeIII(C2O4)3 (A = organic cation), in low and high magnetic fields:: Manifestation of Neel N and Q type ferrimagnetism in a molecular lattice

Detailed bulk magnetization and magnetic susceptibility measurements are reported for representative examples of the series of ferrimagnetic tris-oxalato-ferrate(II,III) salts with general formula AFe(II)Fe(III)(C2O4)(3) (A = quaternary ammonium, phosphonium, or arsonium). The compounds all crystallize in two-dimensional hexagonal honeycomb lattices, but while some show conventional low field positive magnetization at low temperature (Neel type Q), others show a large negative magnetization below a compensation temperature T-comp (Neel type N) under the same measurement protocol. Isothermal and temperature-dependent magnetizations are measured after zero field and field cooling. Temperature-dependent hysteresis measurements are also presented. In compounds that exhibit negative magnetization a discontinuity in the magnetization is observed at T-t(T-comp < T-t < T-c) which correlates with the onset of a giant anistropy and is indicative of a magnetostrictive transition. In compounds that exhibit positive magnetization, hysteresis behavior and frequency-dependent ac susceptibility data indicate a glassy magnetic order at low temperatures, possibly arising from the frustration of random anisotropy domains below a characteristic blocking temperature or imbalance and disorder of Fe(PC) and Fe(III).