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
(M
_i

^z
M
_j

^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 . [
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.