Large metal clusters and lattices with analogues to biology

The magnetic properties of two types of material derived from the brucite lattice, M(OH)(2) are described. The structure-directing effects of simple templates on the brucite lattice parallels the processes seen in nature in formation of biominerals. The first type exemplified by Fe-17/Fe-19 aggregates models the structural features of the iron storage protein ferritin. The magnetic behaviour also reveals some interesting parallels with the magnetic phenomena reported previously on ferritins. We have used a combination of experimental techniques including DC, AC and RF susceptibility measurements on powders and a microSQUID on single crystals. The second type is based on an extended-defect brucite structure with stoichiometry M-2(OH)(2)(ox) for M = Fe2+, Co2+. They show long-range ordering to antiferromagnetic phases and then, at much lower temperatures, undergo a phase transition to canted antiferromagnetic states. Symmetry arguments are used to predict the spin configurations in these extended materials.