Ferromagnetic Ordering in Superatomic Solids

In order to realize
significant benefits from the assembly of solid-state
materials from molecular cluster superatomic building blocks, several
criteria must be met. Reproducible syntheses must reliably produce
macroscopic amounts of pure material; the cluster-assembled solids
must show properties that are more than simply averages of those of
the constituent subunits; and rational changes to the chemical structures
of the subunits must result in predictable changes in the collective
properties of the solid. In this report we show that we can meet these
requirements. Using a combination of magnetometry and muon spin relaxation
measurements, we demonstrate that crystallographically defined superatomic
solids assembled from molecular nickel telluride clusters and fullerenes
undergo a ferromagnetic phase transition at low temperatures. Moreover,
we show that when we modify the constituent superatoms, the cooperative
magnetic properties change in predictable ways.