Microstructure and Exchange Coupling of Segregated Oxide Perpendicular Recording Media

The magnetic properties and corresponding microstructure of (Co ₈₀Pt₂₀)_x (metal oxide)_1-x perpendicular recording media have been studied as a function of the volume percentage (vol%) of metal oxide sputtering into the magnetic film. The exchange coupling field (Hex) estimated from the coercivity (H _c) and nucleation field (H_n) decreases rapidly between 0-20 vol% of metal oxide. The analytical transmission electron microscope composition analysis of (Co₈₀Pt₂₀)_x(TiO₂)_1-x media confirms that the microstructure includes crystalline grain cores in an apparently amorphous oxide matrix. The grain cores comprise only Co and Pt in a nearly constant ratio independent of the vol% of oxide addition. The amorphous matrix contains Co, Ti, and O, but no Pt. The Co concentration is nearly constant in grain boundary and core regions, unlike high-temperature longitudinal recording media wherein Co segregates to form a concentration gradient in the grain core. Perpendicular media thus maintain fairly high anisotropy of the grain core phase, even for very high-oxide concentrations that significantly decrease remanant magnetization (Mrt), Hc, and thermal stability (K_uV/kT)