(07B722) Ferromagnetic resonance analysis of internal effective field of classified grains by switching field for granular perpendicular recording media

摘要

The internal effective fields H_(eff) of granular perpendicular magnetic recording media with a switching field (SF) distribution were measured by ferromagnetic resonance (FMR) by sweeping the external field H_(DC)- H_(eff) consists of the anisotropy field H_k the dipole interaction field, the self-demagnetization field, and the intergranular exchange (coupling) field H_(ex) for up and down magnetic moments of magnetic grains classified by their SF. Prior to the measurement, magnetic grains were classified into two classes: Those with high and low SFs when H_(DC) is swept from + 18 kOe to a negative field. FMR measurements were performed in a range for which the same domain structure was retained for typical strong and weak intergranular exchange coupled media (media I and II, respectively). These measurements revealed the Following points. (1) Resonances originating from majority-direction moments were observed, whereas those of minority-direction moment were not. (2) The increase in H_(eff) with decreasing AnM for medium II is larger than that for medium I. (3) H_(ex) can be expressed as H_k — 4πM —H_(eff) when the sum of dipole interaction field and self-demagnetization field is assumed to be the average field 4πM. H_(ex)/H_k was evaluated to be 0.25 (for grains with low SF) and 0.37 (for grains with high SF) for medium I and 0.09 (for both low and high SF) for medium II under M = 0.