We present results from density functional theory calculations referring to the magnetic properties of 13, 55, 147 and 309 atoms Fe-X (with magnetic Co and Mn or non magnetic Cu substitutions) icosahedral nanoclusters and coating on Cu111 surface in order to stabilize the film in fcc-like structure. Aiming in finding the nanocluster with the optimum magnetic moment (mB) we explored the various sizes considering several compositions and atomic conformations for Fe with Co, Mn and Cu substitutions. Starting with the FeCu nanoclusters, it came out that configurations with agglomerated Fe atoms inside the Cu-Fe and the pure Cu surface shell are energetically favoured while the highest magnetic moment, 3.2 mB on the Fe atom, was found in the Cu12Fe case with the Fe atom located at the surface cell. In addition, increasing the size of the cluster mB converges to the value of the surface Fe atom. The magnetic moment is mainly due to Fe's spin up - down electronic density of states difference close to the Fermi level(EF). In particular, the spin-up Fe d electronic density of states are fully occupied yielding wavefunctions with homogeneous change distribution and Fe 4p occupation while the spin-down is almost unoccupied exhibiting dangling bonding states close to EF. The 13 and 55 clusters are almost half-metallic, while the 147 and 309 cluster exhbit mainly metallic features, in line with the Fe clusters. In all cases the nano-clusters exhibit larger mB than the Fe thin films and bulk systems while the alloy Side cluster's mB was found to decrease towards the Fe monolayer on Cu(111) value, reaching a plateau above 120 atoms.
The structural and magnetic properties of the Fe nanoclusters with magnetic Co or Mn substitutions were also evaluated. Contrary to Cu12Fe, Co12Fe and Mn12Fe are more stable when Fe is in the shell. The Co12Fe total magnetic moment is higher than Co13 and in both cases the spin are coupled ferromagnetic. On the other hand, Mn12Fe total magnetic moment is smaller compared to Mn13 and both cases show a ferrimagnetic behavior. The structural and magnetic properties of the bigger FeCo and FeMn nanoclusters as well as the FeCo/Cu111 and FeMn/Cu111 thin coatings were also evaluated. These results could be used for the design of environmental sustainable smart nanoclusters and coatings with superior magnetic properties suitable for target applications.
This work was supported by the SELECTA (No. 642642) H2020-MSCA-ITN-2014 project.
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