Effect of inhomogeneous microstructure of granular layer on inter granular/inter layer exchange coupling in stacked perpendicular recording media

The effect of inhomogeneous microstructure of granular layer on inter granular/inter layer exchange coupling in stacked perpendicular recording media is studied by varying SiO2 content of CoCrPt-SiO2 granular layer. From cross-section and plane-view TEM observation, it can be concluded that each magnetic grain at cap layer (CL) grows on one magnetic grain of granular layer (GL), and inhomogeneous nucleation site at GL leads to inhomogeneous initial growth of continuous layer at CL. This phenomenon leads to the increase of inter granular coupling fluctuation in CL. Evaluation of inter granular coupling between magnetic grains at GL in stacked media with CL deposited directly on GL shows average and fluctuation of exchange coupling constant of around 2.9 erg/cm² and 0.6 erg/cm². In order to reduce the inter granular coupling, spacer layer (SL) with Pd material was inserted between GL and CL. As a result, average and fluctuation of exchange coupling constant decrease to 1.4 erg/cm² and 0.3 erg/cm² which suggests that by inserting a SL with small ferromagnetic exchange coupling between GL and CL will make it possible to control the inter granular coupling between magnetic grains at GL with CoCrPt-oxide material.