Gadolinium as an accelerator for reaching thermal equilibrium and its influence on the ground state of Dy2GdN@C80 single-molecule magnets

Endohedral fullerenes are perfect nanolaboratories for the study of magnetism. The substitution of a diamagnetic scandium atom in ${\mathrm{Dy}}_{2}\mathrm{ScN}@{\mathrm{C}}_{80}$ with gadolinium decreases the stability of a given magnetization and demonstrates Gd to act as a single atom catalyst that accelerates the reaching of thermal equilibrium. X-ray magnetic circular dichroism at the ${M}_{4,5}$ edges of Gd and Dy shows that Gd affects the ground state. The Gd magnetic moment follows the sum of the external and the dipolar magnetic field of the two Dy ions and compared to ${\mathrm{Dy}}_{2}\mathrm{ScN}@{\mathrm{C}}_{80}$ a lower exchange barrier is found between the ferromagnetic and the antiferromagnetic Dy configuration. The Arrhenius equilibration barrier as obtained from superconducting quantum interference device magnetometry is more than one order of magnitude larger, though a much smaller prefactor imposes the faster equilibration in ${\mathrm{Dy}}_{2}\mathrm{GdN}@{\mathrm{C}}_{80}$. This sheds light on the importance of angular momentum balance and symmetry in magnetic relaxation.