HYSTERESIS, MICROSTRUCTURE, AND MAGNETOOPTICAL RECORDING IN CO/PT AND CO/PD MULTILAYERS

The factors that influence the coercive field H(c) and the shape of the magnetic hysteresis loop for Co/Pt multilayers (MLs), applied as a magneto-optical (MO) recording medium, have been investigated. The hysteresis loop of MLs, made by evaporation of Kr sputtering, became more rectangular when the total film thickness was reduced, i.e., the saturation field H(s) decreased and the nucleation field H(n) increased. H(s) was calculated using a stripe domain model and H(n) was modeled assuming that nucleation took place at a field that destabilized small vestigial magnetic domains. Both models assumed that domain walls can move in the ML film and the agreement with experiment was good. However, these models could not explain the hysteresis loops for the MLs deposited on a thick Pt base layer or made at high sputter gas pressure. These MLs showed a more particulate microstructure and the hysteresis loop was sheared, consistent with magnetic reversal by uniform rotation rather than domain-wall motion. From thermomagnetic recording experiments it was concluded that these latter MLs were less suitable as a MO recording medium because of higher noise in spite of the larger H(c). Co/Pt disks made by either evaporation or Kr sputtering showed lower noise and a higher carrier-to-noise ratio than those deposited on a Pt base layer or made by Ar sputtering.