Optical instrumentation and characterization for magnetooptical recording media

Abstract

This dissertation presents instrumentation developed for the optical characterizations of magneto-optic (M-O) recording media and explores the magneto-optic Kerr effect in optical recording applications. We developed an accurate method to measure the wavelength dependencies of the magneto-optic Kerr rotation angle θ(k), ellipticity ε(k) and reflectivity R and applied it to the characterization of TbFe and TbFeCo rare earth-transition metal (RE-TM) samples and Co/Pt and Co/Pd superlattice thin films. A variable-angle photometric ellipsometer system is developed for the dielectric tensor characterization of the M-O media. A series of Co/Pd samples with different thicknesses are studied for the understanding of M-O Kerr effect. The composition dependencies of the dielectric tensor for both Co/Pt and Co/Pd superlattice samples are measured, and the enhancement of the magneto-optic Kerr effect for these samples is studied. We also characterized many RE-TM samples and some non-magnetic dielectric, organic, sol-gel and metallic thin films. A semiclassical theory is proposed to describe the wavelength dependence of the magneto-optical Kerr effect. The theory takes into account the effects of the spin-orbit interaction, the band structure of the magnetic electrons and the phenomenological elements of the classical Drude model for the dielectric constant. Analytical formulas for the dielectric constants demonstrate explicitly how the Kerr rotation, the ellipticity and the reflectivity are related to the spin-orbit interaction, the band structure and several phenomenological parameters, such as the number density and relaxation timed of the free electrons. This model is applied to the bulk Co materials and the physics of the magneto-optic Kerr effect in these media is studied. Then we apply the theory to our measurements of the wavelength dependence of θ(k), ε(k) and R in a series of multilayered Co/Pt and Co/Pd thin films, covering the range of the 1.2-3.6 eV. With several adjustable parameters we have obtained a satisfactory match between the theory and the experimental data.