Magnetooptical spectra of discontinuous multilayers Co/SiO2 with tunnel magnetoresistance

Magnetooptical spectra of Co(x)/SiO2(y) bilayers and [Co(x)/SiO2(y)](n) mul tilayers consisting of discontinuous ultrathin Co layers, are studied in th e geometry of transverse Kerr effect (TKE). It is found that: (a) the sign, magnitude and spectral shape of the TKE signal strongly depend on the size of Co particles when Co volume fraction is close to the percolation thresh old (x varying between 1.3 and 1.8 nm): (b) the TKE signal in [Co (1.6 nm)/ SiO2 (3.0 nm)l, multilayers at 3.0 eV has the record-high magnitude for Go- based systems, 3 x 10(-2) which exceeds that measured in bulk Co about in a factor of five and in factor of 50 that corresponding to homogeneous Co fi lm of equivalent thickness; (c) the TKE signal of multilayers is nonlinear with respect to both the thickness of the SiO2 spacer y and the number of p eriods n. To explain this anomalous behavior we have calculated magnetoopti cal spectra of bilayers in the framework of macroscopic Fresnel magnetoopti cs and modified effective medium approach for discontinuous Co layers, cons idering them as nanocomposites Co-SiO2. It is shown that magnetooptical pro perties dramatically change when Co volume fraction approaches the percolat ion threshold. (C) 2001 Elsevier Science B.V. All rights reserved.