Cluster-size dependent internal dynamics and magnetic anisotropy of Ho ions in HoM sub(2)N sub(80) and Ho sub(2)MN sub(80) families (M = Sc, Lu, Y)

The paramagnetic NMR study of HoM sub(2)N sub(80)-I sub(h) and Ho sub(2)MN sub(80)-I sub(h) nitride cluster fullerenes (M = Sc, Lu, Y) reveals strong dependence of Ho-induced paramagnetic shifts ( delta super(para)) in super(13)C NMR spectra on the size of the diamagnetic metal in the cluster. In particular, the delta super(para) value in HoY sub(2)N sub(80) is almost doubled in comparison to that in HoSc sub(2)N sub(80). X-ray magnetic circular dichroism studies show that all Ho-nitride cluster fullerenes have the same magnetic ground state of Ho super(3+). Point-charge ligand-field splitting calculations show that the increase of the M super(3+) radius in going from Sc to Y results in a considerable increase of the energy splitting between different J sub(z) states. This leads to a 19% higher magnetic anisotropy of Ho super(3+) in HoY sub(2)N sub(80) than in HoSc sub(2)N sub(80) at 300 K. Variations of the molecular geometry and cluster dynamics with the size of the cluster are found to have even greater influence on delta super(para) values. This work shows that the magnetic properties of the species confined inside the fullerene cages can be tuned using the geometrical factors such as the cluster and the cage size.