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 H-r. The angular dependence of H-r for the dot arrays indicated coherent rotation of the magnetization during nucleation. We estimated the values of the intrinsic remanence coercivity H-o obtained by subtracting the effect of thermal agitation on the magnetization and the stabilizing energy barrier to nucleation E-o / (k(B)T). The variation in H-o as a function of delta and D was qualitatively in good agreement with that of the effective anisotropy field at the dot center H-k(eff) (r = 0), calculated taking account of the demagnetizing field in the dots. The ratio of H-o to H-k(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 H-o / H-k(eff) (r = 0) ratio due to the difference in delta was observed. On the other hand, E-o / (k(B)T) decreased as delta decreased. E-o / (k(B)T) increased slightly as D decreased, but, was not so sensitive to D over the present D range.