A drastic change of magnetization reversal processes in $[\mathrm{C}\mathrm{o}/\mathrm{C}\mathrm{o}\mathrm{O}/\mathrm{A}\mathrm{u}{]}_{20}$ multilayers has been found by polarized neutron reflectometry. For the unbiased state $(T=300\mathrm{}\hspace{0.5em}\mathrm{K}),$ reversal is due to rotation on both sides of the hysteresis loop. In the exchange-bias state $(T=10\mathrm{}\hspace{0.5em}\mathrm{K}),$ rotation is the main mechanism only for increasing fields. For the decreasing field branch, which is in the direction opposite to the bias (cooling field), the mechanism changes to domain-wall motion. A major advantage of the present CoO/Co system is the independence of exchange bias on cooling field orientation.

• Received 15 October 2001

DOI:https://doi.org/10.1103/PhysRevB.65.092407