A new magneto-optic enhancement effect in macroscopic ferrimagnets

Optical and magneto-optic properties at room temperature of Co/sub 1-x/(EuS)/sub x/ evaporated thin films are presented over a wide photon-energy range. Co/sub 1-x/(EuS)/sub x/ belongs to a new class of phase-separated magnetic materials, called macroscopic ferrimagnets, in which two magnetic phases couple antiferromagnetically across the phase boundary. Polar Kerr rotations of up to 2/spl deg/ are observed in Co rich samples (x/spl les/0.3) at photon energies of 4.5 eV. The high Kerr rotation coincides with a distinct decrease in reflectivity suggesting an optical enhancement effect. A model calculation indicates a new type of enhancement based on the relative index of refraction at the phase boundary between the Co matrix and the EuS precipitate particles.