Quantum Tunneling of the Magnetization in Molecular Nanoclusters

The quantum tunneling of the magnetization is a typical mesoscopic effect located at the transition from classical to quantum physics. Molecular clusters are small objects characterized by a small spin compared to single domain particles but significantly larger than the largest spin observable in atoms [1]. In this view it is not surprising that the magnetic properties of molecular clusters have a marked quantum character. On the other side the macroscopic magnetization of these clusters shows bi-stability, hysteresis effects and superparamagnetic behavior [2] as the more classical single-domain particles, so that they are also known as “single molecule magnets”. Molecular clusters are thus placed at the interface between the classic and the quantum domains and have provided an unexpected richness of quantum effects, which have attracted continuously increasing interest [3]. They have the outstanding advantage of being well-characterized systems with identical objects well ordered in a crystal lattice. Physicists are often interested only in the magnetic core of the cluster, relegating the organic part to the role of a diamagnetic matrix. The solution coordination chemistry technique, used to obtain these clusters, is an important feature, as it allows a fine tuning of the structure and physical properties of the clusters [4–7].