Dynamic coercivity and thermal stability of epitaxial exchange spring trilayers

Exchange-coupled hard/soft magnetic nanocomposites have recently found a renewed interest in data-storage application as exchange spring media, also named exchange-coupled composite (ECC). Developed formerly to improve the energy density of a hard magnetic material by an intimate, direct exchange coupling to a soft magnetic phase with high saturation polarization, as exchange spring media, the soft magnetic phase initiates the switching at moderate fields and thus enables the writing of a magnetic bit, whereas the high anisotropy of the hard phase guarantees the desired thermal stability in zero field. Epitaxial SmCo 5/Fe/SmCo 5 trilayers with tunable switching behavior constitute a well-defined model system for studying of the above-mentioned coupling phenomena. We present time-dependent magnetization relaxation data measured at different reversal fields, which allow to compare thermal stability and switching fields for single hard layers and trilayers with varying thickness of the soft layer.