Measurement of perpendicular media anisotropy field with accurate demagnetization correction

Magneto-optical measurements have been applied to determine the anisotropy field of perpendicular media with a well-defined demagnetizing state. The rotation of the perpendicular magnetization component is measured as a function of the in-plane field by the Polar Kerr effect. The field range is sufficiently small to avoid domain formation and ensure coherent magnetization rotation. By fitting to a simple response function, the effective anisotropy field (HK1′=HK1−4πMS) with a well-defined 4πMS demagnetization correction can be determined. This also enables accurate determination of the ratio of short-time coercivity H0 over anisotropy field Hk, an important parameter for perpendicular recording. The H0/Hk ratio is found to decrease with increasing intergranular coupling strength, in good agreement with our micromagnetic results. It drops from about 0.8 for weakly coupled media to 0.5 for strongly coupled media. Theoretical studies show that the effects of easy axis angular dispersion are small, about 1% error for 5° dispersion, and the rotation method measures the mean value of Hk for media with anisotropy field distribution.