Asymmetry in Elementary Events of Magnetization Reversal in a Ferromagnetic/Antiferromagnetic Bilayer

Real-time magneto-optical indicator film images reveal distinct asymmetry in the motion of a single domain wall in a wedged-NiFe/uniform-FeMn bilayer due to the nucleation and behavior of an exchange spring in the antiferromagnetic layer. Magnetization reversal from the ground state begins at the thick end of the wedge where the exchange anisotropy field $\left(H_{\mathrm{E}}\right)$ is minimal and the magnetostatic field $\left(H_{\mathrm{MS}}\right)$ is maximal, whereas reversal into the ground state begins from the thin end where $H_{\mathrm{E}}$ is maximal and $H_{\mathrm{MS}}$ is minimal.