Contrasted role of disorder for magnetic properties in an original mixed valency iron Phosphate

摘要

We have measured the magnetic properties of a mixed valency iron phosphate.It presents an original structure with crossed chains containing Fe II andorthogonal to the longest direction of the crystallites. Microstructuralinvestigations using electron microscopy show the presence of randomnano-twinning. The ac susceptibility measurements demonstrate similarities withthe kinetics of a disordered magnetic, spin-glass like, state but are shown tobe essentially due to this peculiar disorder. Scaling properties arecharacteristics of 3D second order transition implying that this disorder at asmall scale does not influence significantly long range magnetic ordering. Atlow temperature, a decrease of the spontaneous magnetization and anirreversible metamagnetic transition is observed, and is attributed to acanting of the spins in the iron chain.