Role of Media Parameters in Switching Granular Perpendicular Media Using Microwave Assisted Magnetic Recording

This paper describes the role of media parameters in magnetization switching in the presence of a DC bias and an in-plane RF field using a micromagnetic model. In this study, two sets of media parameters are compared for reduction in switching field based on the Larmor precessional frequency of the medium. It is found that a significant reduction in equivalent Stoner Wohlfarth (SW) field (H(SW)(E)) is observed only when a DC field is applied at a finite angle relative to the medium anisotropy direction (theta(A)) and we observe a shallow minimum between 20 degrees and 30 degrees. A small field magnitude H(SW)(E)(= 0.50 H(K)) for theta(A) of 20 degrees for medium I using an RF field magnitude of 0.068 H(K) and an even smaller magnitude H(SW)(E) (= 0.22 H(K)) for theta(A) of 25 degrees for medium 2 using an RF field magnitude of 0.035 H(K) is required to switch the media for the case of a uniform granular medium without any distributions at T = 0 K. With the inclusion of magnetic materials distributions and/or introducing finite temperature, the coherent precession is lost due to the demagnetization field of neighboring grains. We compare H(SW)(E) required to switch the medium in the presence of RF assist to the SW field (H(SW)) required to switch the medium when there is no assist field. It is found that medium 1 shows a reduction of 28% in SW field while medium 2 shows no reduction in presence of in-plane RF field compared to the case when no RF field is applied. This highlights the importance of medium properties in microwave-assisted magnetic recording. Selection of media parameters will depend on the potential application of microwave-assisted recording in a continuous granular or the bit patterned media.