Control of Exchange Coupling Between Granular Oxide and Highly Exchange Coupled Cap Layers and the Effect on Perpendicular Magnetic Switching and Recording Characteristics

We report a systematic study of the switching and recording characteristics of perpendicular magnetic recording media in which the exchange coupling between granular oxide and continuous cap layers was varied. The interfacial exchange coupling strength was controlled by adjusting the magnetization (M_s) and the thickness (t) of the exchange control layer (ECL) between granular oxide and cap layers. The media switching mechanism highly depends on the oxide-to-cap exchange coupling strength as well as the relative moment ratio of cap and oxide layers. Reversal process is coherent for medium with only granular oxide layer and becomes incoherent with incorporation of ECL and continuous cap layers. Optimizing granular oxide-to-cap exchange coupling improves the media writeability as well as the media signal-to-noise ratio (SNR_m). At optimum exchange coupling condition, the switching field is significantly reduced even with higher thermal stability factor (K_u V/k_B T). However, when the interlayer coupling strength is too weak, independent switching of oxide and cap layers occurs, resulting in poor writeability and high media noise. An optimum design of oxide-to-cap exchange coupling is critical in attaining recording properties for high density recording through selection of appropriate ECL and cap materials.