Long magnetic lifetime of a Dy atom on a graphene oxide surface

The presentation of magnetic moment in a long period of time is the key ingredient for the surface supported single atom magnets (SAMs) in potential usages of ultrahigh density magnetic storage and possible realizations of quantum devices. It requires magnetic adatom not only to have the appropriate degenerate magnetic ground states to match with a specific point symmetry of local environment but also to suffer a compatible crystal field (CF) action, prohibiting the quantum tunneling of magnetization (QTM) and maximizing the effective reversal energy barrier (${U}_{\mathrm{rev}}$). We employed the density function theory (DFT) and multiplet simulations as well as the CF Hamiltonian calculations to explore the deposition stability, magnetic moment, and magnetic relaxation of lanthanide adatom (Dy) on an insulating graphene oxide (GO) on Cu(111) substrate. Our DFT calculations revealed that Dy-$sd$ electrons primarily contribute to strong adsorption and the number of $4f$ electrons in the Dy adatom remains the same as that in the isolated Dy atom, labeled as $+\mathrm{II}$ state within $4{f}^{10}$ configuration, which are basically unaffected by Cu(111) substrate. In combination of the simulated x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism spectra (XMCD), and the energy spectrum of magnetic quantum levels, we identified that Dy adatom presents a stable magnetic moment in a long relaxation time and shows a predominant out-of-plane magnetization orientation. The degenerate ground states $|J=8,{m}_{j}\ensuremath{\approx}\ifmmode\pm\else\textpm\fi{}8\ensuremath{\rangle}$ of Dy adatom are protected from the QTM by ${C}_{3v}$ symmetry provided by the substrate CF, while there appears the QTM between the degenerate second-excited states $|J=8,{m}_{j}=\ifmmode\pm\else\textpm\fi{}6\ensuremath{\rangle}$. The spin-flip excitations from $|J=8,{m}_{j}\ensuremath{\approx}\ifmmode\pm\else\textpm\fi{}8\ensuremath{\rangle}$ states to $|J=8,{m}_{j}\ensuremath{\approx}\ifmmode\pm\else\textpm\fi{}7\ensuremath{\rangle}$ states and subsequently the de-excitations to $|J=8,{m}_{j}\ensuremath{\approx}\ensuremath{\mp}8\ensuremath{\rangle}$ states reduce the magnetization reversal barrier from 24.57 to 10.52 meV. We estimated a long magnetic lifetime of 2715 s at 4.5 K, indicating that the stabilized magnetic moments and thus the hysteresis of Dy adatom could be experimentally measured in a liquid helium environment.