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
₀
obtained by subtracting the effect of thermal agitation on the magnetization and the stabilizing energy barrier to nucleation E
₀
/(kBT). The variation in H
₀
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
₀
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
₀
/H
_k

^eff
(r=0) ratio due to the difference in delta was observed. On the other hand, E
₀
/(k
_B
T) decreased as delta decreased. E
₀
/(kBT) increased slightly as D decreased, but, was not so sensitive to D over the present D range