Self-organized magnetic nanoparticles with diameters of less than 10 nm are interesting for technological applications and for the investigation of interface properties due to their high surface-to-volume atom ratio. One of the most important magnetic properties, the magnetic anisotropy energy (MAE) is strongly influenced by the local structure and size of the particles, since on the atomic level MAE is related to the anisotropy of the orbital magnetic moment. Well-known techniques to measure the orbital contribution to the total magnetic moment are ferro-/paramagnetic resonance (FMR/EPR) and x-ray magnetic circular dichroism. Two examples will be discussed: a)disordered 3 nm FePt with different Fe contents, b)11.4 nm CoO@Co (a 2nm CoO shell surrounding a 8 nm Co core). For the FePt particles with different Fe concentration we find a linear increase of the g-factor measured by FMR/EPR , i.e. of the ratio of orbital-to-spin magnetic moment for larger Pt contents. This indicates that the presence of Pt induces an enhanced orbital magnetic moment in the nanoparticle. In the case of CoO@Co we find by FMR a bulk- like g factor g = 2.15 of fcc Co, while XMCD yields a 300 % enhanced ratio of orbital-to-spin moment. A quantitative comparison taking the different sampling depths of both techniques into account reveals the presence of uncompensated large magnetic Co moments at the interface of the antiferromagnetic CoO shell to the ferromagnetic Co core . Supported by EC contract no. HPRN-CT- 1999-00150 and Deutsche Forschungsgemeinschaft.