Tunable dipolar magnetism in high-spin molecular clusters.

We report on the Fe-17 high-spin molecular cluster and show that this system is an exemplification of nanostructured dipolar magnetism. Each Fe-17 molecule, with spin S=35/2 and axial anisotropy as small as D similar or equal to-0.02 K, is the magnetic unit that can be chemically arranged in different packing crystals while preserving both the spin ground state and anisotropy. For every configuration, molecular spins are correlated only by dipolar interactions. The ensuing interplay between dipolar energy and anisotropy gives rise to macroscopic behaviors ranging from superparamagnetism to long-range magnetic order at temperatures below 1 K.