For very thin Co layers, the exchange coupling between adjacent Co layers in $\mathrm{Co}∕\mathrm{Pt}$ multilayers is ferromagnetic and the coupling strength varies nonmonotonically as the nonmagnetic Pt layer thickness $\left(t_{\mathrm{Pt}}\right)$ ranges from $3\text{to}75\mathrm{\AA }$. We report on the magnetization reversal process in a series of ${[\mathrm{Co}\left(4\mathrm{\AA }\right)∕\mathrm{Pt}\left(t_{\mathrm{Pt}}\right)]}_N$ multilayers observed by magneto-optical Kerr microscopy as a function of $t_{\mathrm{Pt}}$ and layer repetition $N$. The images reveal the evolution of magnetic reversal processes that strongly depend on $t_{\mathrm{Pt}}$ and therefore on the interlayer coupling. For $\mathrm{Co}∕\mathrm{Pt}$ multilayers with small $t_{\mathrm{Pt}}$, e.g., $11\mathrm{\AA }$, where the Co layers are strongly coupled, the whole multilayer switches as a single ferromagnet. As Co layers are separated farther and become weakly coupled, e.g., at $t_{\mathrm{Pt}}=41\mathrm{\AA }$, layer-by-layer magnetic reversal is observed. The Kerr images reveal metastable magnetic domain configurations during layer-by-layer switching which is not evident in the measured hysteresis loops during the abrupt magnetic reversal for $\mathrm{Co}∕\mathrm{Pt}$ multilayers with weak interlayer coupling at large $t_{\mathrm{Pt}}$.

• Received 29 December 2005

DOI:https://doi.org/10.1103/PhysRevB.73.224422