Control of exchange coupling for direct overwrite media using Pd metal interlayer

Several kinds of direct overwrite schemes have been proposed for magneto-optic media. Schemes using weakly coupled multilayers have shown great promise. In these methods, control of exchange coupling is key to realizing overwrite. An intermediate layer between the memory and reference layers is used sometimes to control the degree of exchange coupling and interface wall energy density. For this purpose, GdFeCo layer having in-plane anisotropy has been used previously. However, it is easily oxidized. Also, these multilayer direct overwrite media are comprised of similar materials but with different concentrations of components. The components from one layer may diffuse into the adjacent layer, rendering direct overwrite impossible. We found that easily polarizable metals such as Pd can be used as an interlayer to control the degree of exchange interaction between memory and reference layers. Pd metal has no magnetic moment by itself, but a moment is induced on it when it is in proximity to a magnetic material. This induced magnetic moment can mediate the exchange interaction between the reference and memory layers. Since Pd is noble, a very thin layer of Pd (10–20 Å) is stable and prevents diffusion between the magnetic layers.