Magnetooptical spectra of discontinuous multilayers Co/SiO2 with tunnel magnetoresistance

Magnetooptical spectra of Co(x)/SiO2(y) bilayers and [Co(x)/SiO2(y)](n) multilayers consisting of discontinuous ultrathin Co layers, are studied in the 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 threshold (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 film 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 periods n. To explain this anomalous behavior we have calculated magnetooptical spectra of bilayers in the framework of macroscopic Fresnel magnetooptics and modified effective medium approach for discontinuous Co layers, considering them as nanocomposites Co-SiO2. It is shown that magnetooptical properties dramatically change when Co volume fraction approaches the percolation threshold. (C) 2001 Elsevier Science B.V. All rights reserved.