Laser-induced ultrafast spin dynamics in di-, tri- and tetranuclear nickel clusters, and the M process

We present a theoretical investigation of the ultrafast magneto-optical dynamics in clusters with 2, 3 and 4 Ni atoms. We study cooperative effects by increasing both the number of active centers and the multiplicities (up to quintets) in our Hilbert space. In the dinuclear cluster Ni$_2$ a novel spin-flip scenario based on the M process is established\footnote{D. Chaudhuri, H. P. Xiang, G. Lefkidis and W. H\"{u}bner, Phys. Rev. B, in print (2014).}. This process is highly operative in case the standard $\Lambda$ process fails. In the trinuclear cluster Ni$_3$Na$_2$ simultaneous spin-flip and spin-transfer is observed. Local spin-switch is also achieved via a non-linear M process which involves two off-resonant transitions. Finally, in the tetranuclear cluster (Ni$_2$)$_2$ the use of quintets provides an insight into an irreversible demagnetization scenario. We believe that our systematic investigation allows us to establish a relation between the magnetic centers and the multiplicities. Our research represents an important step towards the miniaturization of spintronic devices and functionalization of various logic elements based on molecular structures\footnote{W. H\"{u}bner, S. Kersten and G. Lefkidis, Phys. Rev. B \textbf{79}, 184431 (2009).}.