Impact of Anisotropic Exchange on M-H Loops: Application to ECC Media

Micromagnetic simulation results on Co-based recording media are presented which examine the impact of a modified near-neighbor exchange interaction between grains of the form J(z)((MiMjz)-M-z), reflecting the hexagonal crystal symmetry. Both out-of-plane and in-plane M-H loops are calculated, with an emphasis on a model fit to data reported by Wang et al.. [IEEE Trans. Magn, vol. 43, p. 682 (2007)] on exchange coupled composite perpendicular media. The principle effect of J(z) is to increase the coercivity and slope of both hard and soft layers. Improved agreement with experimental data for the in-plane loops is achieved by assuming a substantial value for J(z). Possibilities for measurement of J(z) through spin-wave excitations are discussed. Thermal fluctuation effects are also examined through simulations of the magnetization vs temperature.