Theoretical study of laser-induced ultrafast spin dynamics in small iron-benzene clusters and of related laser and magnetic-field effects

Using high-level quantum chemistry calculations, we predict various ultrafast laser-induced spin dynamics scenarios in clusters ${\mathrm{Fe}}_{m}{\mathrm{Bz}}_{n}$ ($m,n=1,2$) based on the nonadiabatic $\mathrm{\ensuremath{\Lambda}}$ process---an indirect transition channel from the initial state to the final state through the participation of several spin-mixed intermediate states. The geometry-dependent electronic structures of the four clusters are found to exhibit distinct characteristics, and prove to strongly affect the laser parameters and dynamical behavior of the spin-flip scenarios. For the two Fe-dimer clusters, a charge-transfer state involving spin-transfer scenario is achieved in ${\mathrm{Fe}}_{2}\mathrm{Bz}$, which turns to be much faster than the ordinary one obtained in ${\mathrm{Fe}}_{2}{\mathrm{Bz}}_{2}$, and thus is considered to be promising for future spintronics applications. Furthermore, to provide valuable information for the measurement and implementation of the ultrafast magnetism response, the effects of the full width at half maximum (FWHM) of the laser pulse and the magnitude of the external magnetic field on the proposed spin scenarios are investigated. The analysis of the stability and sensitivity of each scenario shows that the spin-transfer scenarios have smaller tolerance values than spin-flip scenarios with respect to the laser FWHM, and a desired spin scenario is only possible when the magnetic field strength lies in a moderate region. The latter effect enables us to obtain the lateral resolution of the device sample for its possible memory usage and to reach the complementary metal oxide semiconductor scale, beyond the optical resolution limit. All the results in this paper contribute a further step toward the experimental realization of our spin dynamics and their future nanospintronics applications.