| In order to meet the increasing demand for high-density storage and high-speed information processing capabilities,searching suitable nano-scale magnetic materials to achieve ultrafast spin manipulation has become one of the research hotspots in recent years.The transition-metal benzene complexes are considered to be one of the most promising molecular magnet material species due to their unique physical and chemical properties.In this paper,by using the first-principles calculation method,we study the geometric conformation,infrared spectra and electronic structures of magnetic clusters FemBzn(m,n?2),based on which the effects of laser and magnetic field on spin dynamics are further explored.The main contents and results are as follows:Firstly,we perform the Hartree-Fock calculation to optimize the four iron-benzene magnetic clusters.To ensure the stabilities of the obtained structures,frequencies calculations are further performed.The results show that the ground states of the four clusters are all triplet with(half-)sandwich configurations.The calculated benzene-related vibrational frequencies show a decent agreement with experiment,with the modes of the benzene ring breathing and C-C-C bend being red shifted,and the plane C-H bend and C-H stretching modes being blue shifted.Then,the more accurate ground and excited many-body states of the systems are obtained by applying the symmetry-adapted cluster configuration interaction method.After including the spin-orbit coupling and adding a static magnetic field,the?-process-based ultrafast spin dynamics on iron-benzene magnetic clusters are explored under the influence of the well tailored laser pulses.It's found that an additional Fe atom can introduce stronger 3d electron correlations and produce more d states,while an additional benzene ring can give rise to stronger 3d-? electron interactions due to the inductive-I effects and result in more charge transfer states.The different energy distributions of the clusters will cause different spin dynamics features.For the ultrafast spin-flip scenarios,the laser energies for driving spin flip in clusters Fe1.2Bz are lower than those for the corresponding Fe1,2Bz2 ones.For the two ultrafast spin-transfer scenarios obtained in clusters Fe2Bz and Fe2Bz2,one is accompanied with charge transfer and the other is reversible.Based on these scenarios,the effects of full width of half maximum(FWHM)of the laser pulse and the magnetic field strength on them are investigated for the purpose of guiding future experimental implementations.We find that the derivation from the resonant FWHM within a moderate range always causes a decrease of the fidelity.In general,spin-flip scenarios have larger tolerance values than spin transfer with respect to the laser FWHM,indicating the fact that they are easier to be realized in experiment.In addition,when the FWHM is an integer multiple of the resonant FWHM,the fidelity of the spin flip behaves similarly to the oscillation of the initial and final states of the two-level system under the resonant Rabi frequency.The study of magnetic field effect shows that high fidelity of the spin dynamics can be achieved only within a suitable range of magnetic field strength.Too small and too large values always bring about low fidelity,the former is due to the indistinguishability of the states,and the latter is due to the Paschen-Back effect,which leads to the weakening of the spin-orbit coupling and level crossing.Based on the fact that different spin dynamics show different sensitivity to the magnetic field strength,we could apply this sensitivity to obtain the lateral resolution of a certain sample device and achieve the purpose of accurate storage and writing.The study of the laser-induced ultrafast spin dynamics in FemBzn(m,n?2)clusters could provide theoretical guidance and valuable reference for the future experimental realization and spintronic device design,and promote the related applications and development in high-density storage and quantum calculating. |
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