A complex transverse ac susceptibility (chi_T) technique based on magneto-optical detection has been developed with sufficient sensitivity for thin-film recording media. The technique has been used to measure the dispersions in grain size and the anisotropy field of perpendicular magnetic recording media. Experiments have been designed to study the key factors contributing to the anisotropy field distribution (sigmaHk) in perpendicular media. The correlation between anisotropy dispersion, stacking faults, and recording performance have also been studied. A good correlation between stacking faults and sigmaH_K has been established. Lower stacking faults result in smaller anisotropy distribution and better media signal-to-noise ratio. The main factors controlling stacking faults are studied. Theoretical studies of the effect of interactions on the chi_T are also presented