Asymmetric Magnetization Reversal in Exchange-Biased Hysteresis Loops

Polarized neutron reflectometry is used to probe the in-plane projection of the net-magnetization vector $\overrightarrow{\mathrm{M}}$ of polycrystalline Fe films exchange coupled to twinned (110) $\mathrm{MnF}{}_2$ or $\mathrm{FeF}{}_2$ antiferromagnetic (AF) layers. The magnetization reversal mechanism depends upon the orientation of the cooling field with respect to the twinned microstructure of the AF, and whether the applied field is increased to (or decreased from) a positive saturating field; i.e., the magnetization reversal is asymmetric. The reversal of the sample magnetization from one saturated state to the other occurs via either domain wall motion or magnetization rotation on opposite sides of the same hysteresis loop.