The increase in computation capability has made the prediction of magnetic anisotropy in complex molecular structure a precious tool for a rational design of Single-Molecule Magnets with enhanced magnetic bistability. Simpler models based on the modellization of the ligand field, for instance using approximate point charge distributions, are also very useful because of their capability to extract direct magneto-structural correlations. Much less efforts are instead devoted to the experimental determination of the magnetic anisotropy, which would actually require an accurate determination of both its strength and orientation. The second aspect, often underestimated, is of particular relevance in polynuclear systems where spin non-collinearity can lead to high order transverse anisotropy, particularly efficient in promoting quantum tunneling, or even more exotic phenomena, like toroidal arrangement of the magnetic moments.<br/>Single crystal magnetometry is a precious tool particularly for EPR-silent systems, but its success is reduced when more than one molecular orientation are present in the crystal lattice. We have recently employed torque magnetometry based on sensible capacitive cantilever to investigate mononuclear and polynuclear systems. The advantages of the technique are really remarkable: first of all the high sensitivity allows to extend the investigation to crystals of the same size as those employed for X-ray diffractometry. It is particularly sensitive at high magnetic field, where it is relatively easy to disentangle the contribution of differently oriented species. For lanthanide-based systems the technique is so sensitive to be usable also for the investigation of ultra-thin films. The fact that the technique is only sensitive to the anisotropic components allows to extend the investigated temperature range towards high temperature. The technique can thus complement luminescence spectroscopy providing information on the energy separation of the excited states.<br/>We will present our recent investigations where we have employed a multi-technique approach to accurately investigate the magnetic anisotropy, revealing also that not always the slow relaxation of the magnetic moment can be associated to the presence of an anisotropy barrier.<br/>* This work has been supported by the European Research Council through ERC-AdG MolNanoMas.

Accurate experimental determination of magnetic anisotropy for a rational design of single-molecule magnets

250th National Meeting (2015)

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