Several series of Mn based multilayers (Mn/SnO(2),Mn/Si, and Mn/SiO(2))(N) were prepared by magnetron sputtering on Si(100) substrates at room temperature (RT). A ferromagnetic phase with T(C) above 300 K is detected only for Mn/SnO(2). The highest ferromagnetic signal corresponds to the presence of Mn in a mixed valence state combined with the presence of tin oxide. Grazing incidence high-angle x-ray diffraction revealed the formation of MnO and SnO(1+x) nanocrystals. After annealing, no traces of metallic Mn or MnO are detected from x-ray absorption near-edge structure (XANES) or diffraction; Mn(2)O(3) and Mn(3)O(4) oxides and polycrystalline SnO(2) were identified. A clear ferromagnetic signal below 42 K with high coercive field is then detected corresponding to Mn(3)O(4) but the RT ferromagnetic component decreases drastically. No mixed Mn-Sn-O phases are detected in as-grown or annealed samples. The close vicinity of MnO(1+x) and SnO(1+x) nanograins at the multilayer interfaces seems to be the condition necessary for the RT ferromagnetism. (c) 2008 American Institute of Physics.