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 4M 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 4M. 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.
ASJC Scopus subject areas
- Physics and Astronomy(all)