Switching field distribution of CoPtCr-SiO₂perpendicular recording media obtained by subtracting thermal agitation of magnetization

The effect of thermal agitations on the switching field distribution (SFD) of CoPtCr-Si0₂ perpendicular media was investigated, and the “intrinsic” SFD caused by variations in the grain-to-grain switching field was determined. DC demagnetizing (DCD) magnetization curves and minor DCD (M-DCD) magnetization curves were measured at applied field-sweep rates of ~ 10 Oe/s and ~ 10⁸ Oe/s. We estimated the SFD from the difference between the DCD and M-DCD curves, and defined them as ΔH_r/H_r (at ~ 10 Oe/s) and Δ H^p_r /H_r^p (at ~ 10⁸ Oe/s). The values of Δ H_r/H_r were much larger than those of ΔH_r^p/H_r^p. Moreover, Δ H_r/H_r increased faster than ΔH_r^p /H_r^p as the thickness decreased, suggesting that the SFD measured at vibrating sample magnetometer (VSM) time scales is significantly influenced by thermal agitation. The intrinsic SFD estimated using a series of media with various film thicknesses was about 0.14, which was 55%-75% of ΔH_r/H_r for 8-16-nm-thick media. An analysis of the temperature dependence of ΔH_r/H_r supported this conclusion. It is concluded that the SFD measured at VSM time scales is significantly influenced by thermal agitation of the magnetization, and the intrinsic SFD is likely to be nearly half that measured at VSM time scales.