Systematic Investigation of the Annealing Behavior of Magneto-optical Discs

A comprehensive study of the annealing behavior of magneto-optical disc substrates was performed, offering important insight into the origin of birefringence. The lateral birefringence is a result of the flow-induced molecular orientation in the skin layers generated in the mold filling stage, and the cooling-induced energy-elastic stresses generated inside and outside the mold. Cooling-induced energy-elastic birefringence relaxes quickly, and consequently the flow-induced birefringence with a radial dependence of decrease at the outer radius becomes predominant after annealing below the glass transition temperature. The annealing behavior of the vertical birefringence follows a Kohlrausch-Williams-Watts-type relaxation. The results serve as a predictive tool for similar substrates.