Effect of thermal agitation on the switching field distributions of CoPtCr–SiO₂ perpendicular recording media

The effect of thermal agitations on the switching field distribution (SFD) of CoPtCr–SiO₂ perpendicular media was investigated. Dc demagnetizing (DCD) magnetization curves and minor dc demagnetizing (M-DCD) magnetization curves were measured at applied field sweep rates of ∼10 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 ΔH_r^P/H_r^P (at ∼10⁸ Oe/s). The values of ΔH_r^P/H_r^P were found to be 60%–70% of ΔH_r/H_r. The difference between ΔH_r^P/H_r^P and ΔH_r/H_r should be caused by thermal agitation of the magnetization. The influence of the distribution of the thermal agitation on SFD was calculated using the distribution of the grain volumes. It is concluded that the SFD measured at vibrating-sample magnetometer (VSM) time scales is significantly influenced by thermal agitation of the magnetization, and reduction of the grain size distribution is the most effective way to reduce the SFD at VSM time scales.