Theory of laser-induced ultrafast magneto-optic spin flip and transfer in charged two-magnetic-center molecular ions: Role of bridging atoms

Abstract

Laser-induced ultrafast spin manipulations in positively charged two-magnetic-center molecular ions with a small number of bridging atoms are investigated to explore the role of bridging atoms in the spin switching process and spin transferability between the magnetic centers via the Λ process. Taking O and Mg as examples for bridging atoms, fully ab initio calculations demonstrate that spin flip can be readily achieved on subpicosecond time scales at both magnetic centers of the linear structures composed of two nonidentical magnetic atoms with a single bridging atom in between. Although these two nonmagnetic elements possess completely different chemical and electronic natures, both types of bridging atoms contribute to spin density redistribution at the magnetic atoms, especially for the low-lying triplet states that are suitable to act as initial and final states in the Λ-type process of spin flip or transfer. This also provides a rule-of-thumb that spins in the linear structures can be flipped more easily since symmetric structures exhibit weaker magnetocrystalline anisotropy. The spin transfer process achieved in the structure [Fe-O(Mg)-Co] + demonstrates that if both bridging atoms are involved to further lower the symmetry of the linear structures, spin transferability between the Fe and Co atoms can be improved.

Analytical treatment of ultrafast laser-induced spin-flippingΛprocesses on magnetic nanostructures

“…Furthermore, this analytical model is capable of describing laser-induced spinflipping processes on magnetic materials with triplet ground state and strongly localized spin density. Such materials can comprise, among others, linear or branched metallic chains deposited on inert surfaces, [9][10][11] metallic clusters in the gas phase (with or without chromophores such as CO as experimental magnetic-state markers), 12 and ligand-stabilized complexes in solution. 13,14 For the time evolution of the system, we use a wave function rather than a density-matrix approach exploited by other authors (see Refs.…”

Strain Effect on the Ultrafast Spin Switching of Cobalt-Doped Carbon Fullerenes

“…In numerous ultrafast, laser-induced, magnetization-dynamics scenarios we have already demonstrated that Λ processes can act as exact microscopic spin-transition mechanisms on various bare and ligand-stabilized molecular systems [25]- [27]. In our previous studies we demonstrated that this theoretical model is also effective for the endohedral fullerenes [28], [29].…”

Coherent ultrafast local spin-switching Λ processes in chainlike nanostructures with two identical magnetic centers

“…Our own codes are implemented in the last two steps for the computation of the SOC, the coupling to the static external magnetic field, the time propagation during the spin-switching processes, the optimization of the laser pulse (genetic algorithm), and the global search for the intermediate states involved in the ultrafast L process [22]. The step-by-step description of the equations and computational details can be found elsewhere [27,34].…”

“…have different local symmetry) [24]. We know that in the second case there is a much higher degree of spin-density localization, as investigated in our recent work [27], while in the first case, at least theoretically, both active centers will always carry an equal amount of spin density, rendering any spin-manipulating process nonlocal. At the same time we know that in order to induce a L process the states G 1 and G 2 need to be quasidegenerate.…”

“…The combination of these two general rules implies that it is easier to induce a spin-transfer scenario when the two active centers are similar but not identical. This is partially the motivation of this work (distinct from previous works [27]), namely to investigate, as a first step, to which extent structures with two identical active centers can exhibit a high degree of spin localization and allow for local spin-flip scenarios. A further motivation stems from the fact that structures with fewer atom types are typically easier to synthesize and handle (e.g.…”