Imaging the Magnetization Processes in Epitaxial Exchange Coupled SmCo /Fe/SmCo Trilayers

A detailed understanding of the magnetization processes in an exchange coupled SmCo 5 /Fe/SmCo 5 trilayer is derived from imaging the domain configuration of the sample in a succession of remanent states by magnetic force microscopy. Domain nucleation and domain wall movement processes are identified and are interpreted in terms of the dominating coercivity mechanism. As in single hard magnetic SmCo 5 layers, strong pinning of domain walls governs the magnetization reversal and determines coercivity. The coupling to the Fe layer, however, leads to an increased domain size in the thermally demagnetized state and to a larger nucleation density prior to the irreversible magnetization switching. Due to slightly different switching fields of the two SmCo 5 layers, a compensated state can be adjusted, in which the moments of the Fe layer form 180 ° spin spirals with laterally varying chirality. The magnetic contrast arising from these spin spirals is imaged and the irreversible changes in a small in-plane field perpendicular to the easy axis are studied.