Ferrimagnetism in dicarboxylate-bridged cobalt hydroxide layers

Abstract

The synthesis, characterisation (XRD, DTA, IR, UV-Vis) and magnetic properties of the layered compound Co ₅ (OH) ₈ (O ₂ CC ₄ H ₈ CO ₂ )·5H ₂ O are reported. It is characterised by a triangular magnetic lattice with a metal–metal distance of 3.1 Å and an interlayer distance of 14.3 Å. The layers are bridged through the carboxylate groups of the adipate anions. Long range ferrimagnetic (three octahedrally coordinated cobalt centres with spin α and two tetrahedrally coordinated cobalt centres with spin β) ordering is characterised by spontaneous magnetization, an out-of-phase component in the AC susceptibility and a hysteresis loop. The Curie temperature is 52 K and the coercive field is 11 200 Oe at 2 K. Complete reversal of moment to the expected saturation of 3 µ _B was not observed due to the large anisotropy field. The long range ordering does not depend on whether the layers are covalently linked, confirming therefore the importance of dipolar interaction between layers having large effective moments as a consequence of short range intralayer interactions. The large coercive field is due to perpendicular alignment of the moment with respect to the layers and the synergy of crystalline shape and single ion anisotropies.