Enhancement of the Kerr effect in Co-Ag granular films near the plasma edge

A series of CoxAg100-x granular films was annealed at 100, 250, 400, and 50 0 degrees C. Both the dielectric function and the polar Kerr-effect spectra were measured using a spectroscopic ellipsometer and a magneto-optical spe ctrometer in the 1.5- to 4.5-eV photon-energy range. It was found that the Kerr effect was greatly enhanced by increasing the annealing temperature, e specially for those samples having low Co compositions. After annealing, st rong resonance peaks appeared in the 3.7- to 4.1-eV range for low Go-concen tration thin films. In terms of the optical constant and the magneto-optica l quantity E-xy, the line shape of the Kerr spectrum and its origin were an alyzed. The peaks are attributed to joint contributions from the plasma osc illation and the onset of the interband transition mainly related to the ba nd structure of the enlarged Co and Ag particles in the granular film after annealing.