Magnetic properties of cobalt clusters deposited on MgO substrates by molecular beam epitaxy (abstract)

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We report on the preparation and characterization of clusters of Co deposited on MgO(001) and MgO(110) substrates. The preparation is by cell evaporation in ultrahigh vacuum. The size of the clusters is controlled by the substrate temperature and deposition rate or, after deposition, by annealing. This results in clusters with diameters 100–1500 Å and heights 30–200 Å. The characterization is by Rutherford backscattering, photoemission spectroscopy, and atomic force microscopy. The magnetic properties have been investigated by SQUID magnetometry. Depending on the size of the clusters, we have observed superparamagnetic or ferromagnetic behaviors. When the cluster diameter is much smaller than its height, the magnetization is much easier for in-plane fields, due to the demagnetization energy. In some of the samples, we have combined clusters of Co and nonmagnetic Ag, with sufficient density for metallic percolation, and we present their magnetoresistance properties. Journal of Applied Physics is copyrighted by The American Institute of Physics.