Fully epitaxial, exchange coupled SmCo5/Fe/SmCo5 trilayers

Fully epitaxial SmCo5(25 nm)/Fe/SmCo5(25 nm) trilayer films were prepared, in which the easy magnetization axis of both hard magnetic SmCo5 layers is uniquely aligned along one orientation within the film plane. The interlayer exchange coupling between the hard and soft magnetic phase is studied by hysteresis measurements in the magnetic hard and magnetic easy orientation and by dc-demagnetizing loops for different thicknesses of the soft Fe layer. The good coupling together with the optimum texture provided by the epitaxial growth lead to excellent magnetic properties. Fully coupled trilayers are achieved for 6 nm thin Fe layers, which maintain a square hysteresis with high coercivity of μ0Hc = 1.5 T and a 30% remanence enhancement over a single hard magnetic layer. For thicker Fe layers (16 nm) the exchange coupling leads to reversible rotation processes within the soft phase before the trilayer switches irreversibly at a field of 0.9 T. The still acceptable coercive field and the further improved remanence lead to a maximum energy density of 224 kJ m-3 (28 MG Oe). The specific epitaxial relation between SmCo5 and Fe with its unique orientation of the SmCo5 easy axis throughout the whole layer stack presents the essential step in the realization of thick, textured, exchange coupled multilayers with high energy density