The possibility of selective magnetization switching in a three-layered stacked magnetic pillar was discussed using micromagnetic simulation that considers three-dimensional magnetic recording. Selective magnetization switching is possible with the assistance of a circularly polarized microwave field with an adequate corresponding frequency. This study demonstrates that the value of the saturation magnetization of the magnetic layers is critical in suppressing selective magnetization switching errors caused by magnetostatic fields. A relatively large saturation magnetization of up to 600 emu/cm3 in the second layer also allows successful selective magnetization switching, thus enabling three-dimensional magnetic recording. However, damping constants smaller than 0.1 for the magnetic layers are crucial in the model calculations because of the limited strength of the microwave fields applied to the stacked magnetic pillar. The leakage flux is also estimated considering a multi-bit reproducing process, where eight-digit signals are obtained depending on the magnetization states of the stacked magnetic pillar.

The potential of microwave-assisted magnetic recording on exchange-coupled composite (ECC) media is investigated by numerically simulating read/write processes with respect to the physical and magnetic properties of the soft section of ECC media. To obtain desirable recording performance, the thickness of the soft section must be comparable to the exchange length. Under such condition, the optimal microwave frequency decreases owing to the non-uniformity of the reversal mode. A relatively high anisotropy field in the soft section produces high signal-to-noise ratios. Moreover, large saturation magnetization of the soft section enhances the magnetization reversal of ECC grains but excessive enhancement is likely to induce wide writing, which decreases the high track density.

Magnetization mechanisms of nanoscale magnetic grains greatly differ from well-known magnetization mechanisms of micrometer- or millimeter-sized magnetic grains or particles. Magnetization switching mechanisms of nanoscale exchange-coupled composite (ECC) grain in a microwave field was studied using micromagnetic simulation. Magnetization switching involving a strongly damped or precessional oscillation was studied using various strengths of external direct current and microwave fields. These studies imply that the switching behavior of microwave-assisted magnetization switching of the ECC grain can be divided into two groups: stable and unstable regions, similar to the case of the Stoner-Wahlfarth grain. A significant reduction in the switching field was observed in the ECC grain when the magnetization switching involved precessional oscillations similar to the case of the Stoner-Wohlfarth grain. This switching behavior is preferred for the practical applications of microwave-assisted magnetization switching.