Magnetization reversal and defects in Co/Pt multilayers

(Co 3 Å/Pt 10 Å)×N (N=8, 16, and 30 bilayers) multilayer thin films were prepared by sputtering onto an 850-Å-thick SiN layer that had been deposited on a silicon (111) substrate. We used the polar Kerr effect to measure the time dependence of magnetization reversal over the temperature range 90-300 K. Direct domain observations were also carried out. The results show that the domain expansion process depends strongly on the number of bilayers. Uniform domain expansion was found only in the thinner samples. From the time dependence of the magnetization reversal measurements over the temperature range 90-300 K, the activation energy and volume associated with domain wall motion were found to be 1.2 eV and 2.3×10^-18 cm³ for N=8 sample. The N=16 and N=30 samples seem to have a broad distribution of activation energies. Our observations suggest that both the coercivity and magnetization reversal are controlled by the defects that come from the interface between the Co and Pt.