Magnetization reversal in exchange-biasedNi∕NiOlayered structures

Abstract

The dependence of the asymmetric magnetization reversal, exchange field, and coercive field on the NiO microstructure and thickness is studied in polycrystalline $\mathrm{Ni}∕\mathrm{Ni}\mathrm{O}$. Probing structural properties in real and reciprocal space, we show that the modification of the NiO growth conditions results in nonstoichiometric NiO. Exchange and coercive fields are strongly enhanced in nonstoichiometric $\mathrm{Ni}∕\mathrm{Ni}\mathrm{O}$ bilayers. Probing exchange properties in trilayers, we show that the coercive and exchange field enhancements are of different origins but depend on the NiO domain state. Modifying the internal part of the antiferromagnet allows a control of the exchange properties. Studying the Ni magnetization reversal, we reveal the contribution of nonuniform reversal modes and coherent rotation as a function of the angle between the applied field and the Ni easy axis. We observe two distinct critical angles revealing the significant role of nonuniform magnetization reversal in the asymmetry and its angular dependence.