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

Abstract

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