Magnetic molecules are among the last to have joined the list of molecular materials, but have already attracted great attention and are extremely promising candidates as nanoscale memory cells. In fact a peculiar class of molecules, ubiquitously known with the evocative term of Single Molecule Magnet (SMM), has an intrinsic magnetic bistability that is not associated to cooperativity. The “memory effect” of SMM, which is reminiscent of the behavior of single domain magnetic particles, is also accompanied by fascinating quantum effects tanks to the intrinsic quantum nature of these small objects and also to the rigorous mono-dispersity in shape, dimension, and structure.

To fully exploit the advantage of the bottom-up approach typical of molecular sciences organization of SMM on surfaces, is a necessary condition to address the magnetic state of a single molecule. Rather unsurprisingly many studies have been devoted to the Mn₁₂ family of magnetic molecules, [Mn₁₂O₁₂(RCOO)₁₆(H₂O)₄], the archetype of SMM behaviour. However, the complex nature of SMM and the peculiar origin of their magnetic bistability have for half a decade represented an obstacle for the development of this research field.

Thanks to the surface sensitivity, element, and oxidation state selectivity of some synchrotron radiation techniques, i.e. X-ray absorption and X-ray Magnetic Circular Dichroism, it has been shown that the Mn₁₂ clusters are strongly reduced during the process of grafting to a conducting surface. Fortunately another class of polynuclear SMM clusters, based on a propeller-like tetranuclear iron(III) core, Fe₄, demonstrated a more “robust” SMM behaviour, with the typical hysteresis persisting also when the molecules are chemically grafted to on a conducting substrate, like a Au(111) surface, through “alligator clips” (flexible and non-conjugated aliphatic chains terminated with a sulphur-containing group).

These recent findings, combined with an exceptional robustness of these SMM that can be evaporated in high vacuum, open the perspective of using mono or multilayer of SMM in spintronic applications thereby permitting to play with the elementary interactions between electron transport and magnetism degrees of freedom at the molecular scale.

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