Ultrafast spin dynamics in double-magnetic-center endohedral fullerene Y<sub>2</sub>C<sub>2</sub>@C<sub>82</sub>-<i>C</i><sub>2</sub>(1)

Spin switching and spin transfer are essential prerequisites for designing the spin-logic devices based on endohedral fullerenes. In this paper by combining the theoreticalΛ-process model with a self-designed genetic algorithm, we are able to theoretically observe spin-switching and spin-transfer scenarios on the subpicosecond time scale in the endohedral fullerene Y₂C₂@C₈₂-<i>C</i>₂(1) from first principles. The results show that the geometry of the optimized enclosed Y₂C₂ cluster is consistent with the experimental data. There exists a certain repulsive force between the external C₈₂-<i>C</i>₂(1) cage and the encaged cluster. However, the whole system still maintains its integral cage structure due to the excellent stability of the fullerene. In the Y₂C₂@C₈₂-<i>C</i>₂(1) system, it is found that the spin density is highly localized on the two Y atoms and only minimally distributed on the carbon cage. By analyzing the spin-density distribution and the evolution of the spin expectation values as influenced by the laser pulses, it is found that global spin switching can be achieved on the two Y atoms, while spin transfer between the two Y atoms actually results from the redistribution of the spin density among the two magnetic centers and the carbon cage under the action of the optimized laser pulses. The achieved spin-switching scenario completes within about 1000 fs and its fidelity reaches 97.8%, while the obtained spin-transfer process completes within 200 fs and its fidelity reaches 95.1%. The electron absorption spectra of the system verify that optical transitions are possible between the main intermediate states and the initial and final states involved in the spin-switching and spin-transfer scenarios. Therefore, by analyzing the electron absorption spectra corresponding to the initial and final states, the energy of the laser pulses adopted for the studied spin-dynamics process can be predicted, and the spin transferability can be evaluated. In addition, it is found that the smaller the detuning between the required energy difference and the applied laser pulse energy is, the greater the probability for spin switching/transfer scenarios becomes. The present results reveal the mechanisms of the laser-induced ultrafast spin dynamics in Y₂C₂@C₈₂-<i>C</i>₂(1) and can provide a theoretical basis for designing the spin-logic devices on realistic endohedral fullerenes.