Reversible magnetization processes and energy density product in Sm–CoFe and Sm–Co/Co bilayers

The hysteresis properties of epitaxial SmCo/Co and SmCo/Fe bilayers are calculated by the solution of the Landau–Lifshitz Gilbert equation. The thin film grain structure is taken into account using appropriate finite element techniques. The J(H) curve shows the typical exchange spring behavior for the bilayer if the soft magnetic layer thickness exceeds 10 nm. However, the reversible rotations of the magnetization for low external field deteriorate the maximum energy density product. Straight B(H) curves are obtained only for a Fe layer thickness of 5 nm. Magnetization reversal starts with the reversible rotation of the soft layer magnetization. Initially, the magnetization rotates in opposite directions in different regions of the film. The reversible rotations penetrate substantially into the hard layer.