Magnetization of the Layer Compounds AFe^IIFe^III(C₂O₄)₃ (A = Organic Cation), in Low and High Magnetic Fields:  Manifestation of Néel N and Q Type Ferrimagnetism in a Molecular Lattice

Abstract

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 AFeIIFeIII(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 (Néel type Q), others show a large negative magnetization below a compensation temperature T comp (Néel 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 anisotropy 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(II) and Fe(III).

Layered Mixed-Metal Phenylphosphonates, MnxCo1−x(O3PC6H5)·H2O: Structure and Magnetic Properties

“…The negative magnetization shifts observed for the Co-rich specimens contrast with the positive magnetization shifts detected for the Mn-rich materials. The phenomenon of negative magnetization has been identi"ed previously in a variety of ferrimagnetic materials (41,42). Naturally with the doped Co-rich specimens, similar arguments may be made if small regions of ferrimagnetic ordered phase are present.…”

“…For example, in some cases, but not all, the combination of random mixing and magnetic frustration leads to spin glass behavior (40). In addition, some ferrimagnetic systems have exhibited the interesting e!ect of negative magnetization (41,42). New examples of mixed-metal magnetic systems, either structurally ordered or as solid solutions, can provide the opportunity to further study some of these phenomena.…”

A magnetisation and Mössbauer study of triazole (M1−x2+Mx3+)M3+F5(Htaz)1−x(taz)x weberites (M = Fe, Co, Mn, Zn, Ga, V)

“…35 Variations of the magnetic properties were already encountered for slightly different sample compositions of mixed valence iron oxalates with negative magnetisation. 39 They were explained by the existence of structural disorder (stacking faults in N(n-C3H7)4[Fe 2+ Fe 3+ (C2O4)3]) and nonstoichiometry, which are influenced by the preparation method. 40 In the case of .…”

Polarized neutron diffraction and Mössbauer spectral study of short-range magnetic correlations in the ferrimagnetic layered compounds(PPh4)[<

“…Further, in all cases, the unconstrained ratio of iron͑II͒ to iron͑III͒ spectral areas is close to 50:50 in agreement with the small iron͑II͒ deficiency observed experimentally in these compounds. 23 The 0 K extrapolated values of the iron͑II͒ percentages are 48% and 45% in (NBu 4 )Fe 2 (ox) 3 and (PPh 4 )Fe 2 (ox) 3 , respectively.…”