Switching field and thermal stability of CoPt/Ru dot arrays with various thicknesses

The switching fields and thermal stability of CoPt/Ru dot arrays with various dot thickness delta (5-20 nm) were experimentally investigated as a function of the dot diameter, D, (130-300 nm). All dot arrays showed a single domain state, even after removal of an applied field equal to the remanence coercivity Hr. The angular dependence of Hr for the dot arrays indicated coherent rotation of the magnetization during nucleation. We estimated the values of the "intrinsic" remanence coercivity H0 obtained by subtracting the effect of thermal agitation on the magnetization and the stabilizing energy barrier to nucleation E0/(kBT). The variation in H0 as a function of delta and D was qualitatively in good agreement with that of the effective anisotropy field at the dot center Hk eff(r=0), calculated taking account of the demagnetizing field in the dots. The ratio of H 0 to Hk eff(r=0) for the dot arrays with delta=10 nm increased from 0.53 to 0.70 as D decreased from 300 to 140 nm, and no significant difference in the H0/Hk eff(r=0) ratio due to the difference in delta was observed. On the other hand, E0/(k BT) decreased as delta decreased. E0/(kBT) increased slightly as D decreased, but, was not so sensitive to D over the present D range