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Ni-based nanoalloys: Towards thermally stable highly magnetic materials

Molecular dynamics simulations and density functional theory calculations have been used to demonstrate the possibility of preserving high spin states of the magnetic cores within Ni-based core-shell bimetallic nanoalloys over a wide range of temperatures. We show that, unlike the case of Ni-Al clusters, Ni-Ag clusters preserve high spin states (up to 8 $μ_{\mathrm{B}}$ in case of Ni$_{13}$Ag$_{32}$ cluster) due to small hybridization between the electronic levels of two species. Intriguingly, such clusters are also able to maintain geometrical and electronic integrity of their cores at temperatures up to 1000 K (e.g. for Ni$_{7}$Ag$_{27}$ cluster). Furthermore, we also show the possibility of creating ordered arrays of such magnetic clusters on a suitable support by soft-landing pre-formed clusters on the surface, without introducing much disturbance in geometrical and electronic structure of the cluster. We illustrate this approach with the example of Ni$_{13}$Ag$_{38}$ clusters adsorbed on the Si(111)-(7$\times$7) surface, which, having two distinctive halves to the unit cell, acts as a selective template for cluster deposition.