We discuss here, an X-ray Absorption Spectroscopy (XAS) study of (Co/Au) and (Au/Co/Au) ferromagnetic nano-dot arrays grown in-situ on self-organized SiGe substrates, using grazing angle shadow deposition as presented earlier for Co. /1/ We characterized the samples by X-ray Photoelectron Emission Microscopy (XPEEM), X-ray Magnetic Circular Dichroism (XMCD) at the Co L-edges in the XAS mode and XMCD-PEEM. Experiments were performed both at ELETTRA and MAX-lab. These dot arrays exhibit a considerable degree of lateral order, are ferromagnetic and single domain at room temperature. Macroscopic magnetic domains composed of several dots are observed. At low Co coverage, for Co/Au dots, dots with an out of plane moment were evidenced by XMCD-PEEM, at room temperature. Indeed, using angular dependent XMCD studies, versus x-ray incidence angle, for dots containing 2.5 ML Co layers on a 5 ML Au buffer grown on top of the SiGe nano-structured template, a strong stable macroscopic out-of-plane remanence, can be directly observed by XMCD at 100K. Such a sample can also be remanently magnetized in the sample plane. At room temperature no stable out of plane macroscopic remanence can be observed, only smaller out of plane domains can be evidenced by means of XMCD-PEEM. With a thicker Co coverage of 6 ML for Co/Au dots, it is found that the magnetization of the dots lies within the surface plane. A study of the Co orbital moment as a function of both Co and Au cap thickness in these (Co/Au) dot arrays reveals a systematic increase of orbital moment, correlated with the appearance of a macroscopic out-of-plane magnetization. This work is supported by the EC as part of the NAMASOS project STRP NMP2/ CT/2003/505 854 .
1. A. M. Mulders, A. Fraile-Rodríguez, D. Arvanitis, C. Hofer, C. Teichert, M. Á. Niño, J. Camarero, J. J. de Miguel, R. Miranda, K. Lyutovich, E. Kasper, S. Heun, A. Locatelli, Phys. Rev. B vol.71, 214 422, 2005.