Ab initio study of ultrafast laser-induced spin flip, spin-flip transfer, and spin crossover in ComBzn+/0 clusters ( m,n=1,2)

We present a fully ab initio study of the laser-induced ultrafast magnetization dynamics in cobalt-benzene clusters ${\mathrm{Co}}_m{\mathrm{Bz}}_n^+/0$ ($m,n=1,2$). It is found that different geometric configurations and $d\ensuremath{-}\ensuremath{\pi}$ interactions of the four structures cause their high-level electronic structures to exhibit distinct characteristics. By using well-tailored laser pulses to propagate the systems via a spin-orbit-coupling enabled $\mathrm{\ensuremath{\Lambda}}$ process, various local/global spin-flip scenarios are achieved within subpicosecond timescales. Besides, a spin-flip-transfer process within around 300 fs is predicted in ${\mathrm{Co}}₂\mathrm{Bz}$. Governed by the Goodenough-Kanamori rules, the simultaneous spin flip and transfer is favored when the two magnetic centers are antiferromagnetically coupled, reflected in the required lowest laser energy and intensity. Most interestingly, we obtain a novel, $W$-process facilitated spin-crossover scenario in the cluster ${\mathrm{CoBz}}⁺$, which offers additional flexibility of designing relevant all spin-based functions such as molecular switches and sensors. The transferability of the latter two scenarios is also analyzed from the optical spectra of the initial and final states. These results provide the precursory guidance for further study of ultrafast magnetization control in more extended metal-aromatic polymers, and also show their great potential in future nanoscale spintronic applications and quantum information processing.