Strong coercivity reduction in perpendicular FePt∕Fe bilayers due to hard/soft coupling

We have prepared perpendicular hard/soft bilayers made of a 10nm L10-FePt layer, which has been epitaxially grown on MgO(100) and a Fe layer with thicknesses of 2 and 3.5nm. The control of the interface morphology allows to modify the magnetic regime at fixed Fe thickness (from rigid magnet to exchange-spring magnet), due to the nanoscale structure effect on the hard/soft coupling and to tailor the hysteresis loop characteristics. Despite the small thickness of the soft layer, the coercivity is strongly reduced compared to the hard layer value, indicating that high anisotropy perpendicular systems with moderate coercivity can be easily obtained.