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The Effect of Hydrogen on the Magnetic Properties of Supported Nano Scale Clusters


We have calculated the structure and magnetic properties of nano scale iron clusters on a
Cu surface with and without adsorbed hydrogen. The goal was to see what effect hydrogen
has on the magnetic properties. The calculations were carried out with plane wave based
density functional theory (DFT) and with the tight-binding Anderson model. The
adsorption sites for hydrogen atoms were found using the simulated annealing technique.
We considered a number of configurations differing in the number of hydrogen atoms and
in their positions. Two trends were found. Firstly, each successive hydrogen atom reduces
the total magnetic moment of the cluster. Secondly, the strength of the effect depends on
the position of adsorbed hydrogen atom, namely the number of nearest iron neighbors is
important. To explain these effects we used Bader analysis in order to decompose the
charge density of the system and examine the change in electronic density at the iron
atoms. It was found that hydrogen atom affects only the nearest neighbors and attracts the
same number of electrons irrespectively of the adsorption site. However, the more iron
atoms the hydrogen atom is bound to, the weaker the decrease of the total magnetic
moment of the cluster. We also calculated the density of states for d-electrons of individual
iron atoms and observed changes near the Fermi level as hydrogen is added. The Anderson
model contains only three parameters which were selected using information found from
the analysis of the DFT calculations. The model then could reproduce the DFT results
quite well.


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