Specific features of magnetooptical spectra of Co/SiO2 hybrid multilayers

Magnetooptical spectra of Co(x)/SiO2(y) bilayers and [Co(x)/SiO2(y)](n) hyb rid multilayers (x and y are the layer thicknesses) are studied in the rang e 1.5-4.0 eV. In these layers, the ultrathin ferromagnetic layers are not c ontinuous but consist of ellipsoidal Co nanoparticles with a concentration near the percolation threshold. It is found that (a) the sign, magnitude, a nd spectral shape of the magnetooptical signal depend strongly on the Co pa rticle size; (b) the signal for the [Co(1.6 nm)/SiO2(3.0 nm)](6) multilayer s at 3.0 eV has a record-high magnitude for Co-based structures, 3 x 10(-2) , which exceeds that for bulk Co about fivefold and about 50-fold that for a uniform Co film of an equivalent thickness; (c) the magnetooptical signal of multilayers depends nonlinearly on the number of periods and the thickn ess of the dielectric layer y; and (d) the dependence of the signal of bila yers and multilayers with x = 1.3 and 1.6 nm on the wavelength is nonmonoto nic and exhibits clearly pronounced extrema. The data obtained for bilayers are attributed to the strong influence of percolation on the optical and m agnetooptical parameters of the structure and interpreted in the framework of the effective medium approximation and macroscopic Fresnel magnetooptics . (C) 2000 MAIK "Nauka/Interperiodica".