Mapping the magnetic anisotropy at the atomic scale in dysprosium single molecule magnets

The anisotropy of the magnetic properties of molecular magnets is a key descriptor in the search for improved magnets. Herein, we prove how a novel analysis approach using single crystal polarized neutron diffraction (PND) provides direct access to atomic magnetic susceptibility tensors. The technique has been applied for the first time to two Dy-based single molecule magnets, showing clear axial atomic susceptibility for both Dy(III)-ions. For the triclinic system, bulk magnetization methods are not symmetry-restricted, and the experimental magnetic easy axes from both PND, angular-resolved magnetometry (ARM) and theoretical approaches all match reasonably well. ARM curves simulated from the molecular susceptibility tensor determined with PND show strong resemblance with the experimental ones. For the monoclinic compound, a comparison can only be made with the theoretically calculated magnetic anisotropy, and in this case PND yields an easy-axis direction that matches that predicted via electrostatic methods. Importantly, this technique allows the determination of all elements of the magnetic susceptibility tensor and not just the easy-axis direction as is available from electrostatic predictions. Furthermore, it has the capacity to provide each of the anisotropic magnetic susceptibility tensors for all independent magnetic ions in a molecule, thus allowing for studies of poly-nuclear complexes and compounds of higher crystalline symmetry than triclinic.