Pinning-assisted out-of-plane anisotropy in reverse stack FeCo/FePt intermetallic bilayers for controlled switching in spintronics

Abstract We study the implications of FeCo underlayer and overlayer on the static and dynamic magnetic properties of FeCo/FePt exchange spring system along with post annealing kinetics. Probing of FePt/FeCo/Si and FeCo/FePt/Si bilayers using high energy synchrotron X-ray diffraction by varying glancing angles unveiled structural variations at the interface, where FeCo is observed to inhibit the crystalline growth of FePt. A soft ferromagnetic in-plane behaviour and defect-driven hard ferromagnetic properties in the out-plane configuration are established. Besides, the magnetization dynamics studied by Ferromagnetic Resonance depicts an out-plane magnetization component of FePt only in FeCo/FePt/Si. X-ray Absorption Spectroscopy (XAS) in the Fe, Co and Pt L-edge regions reveal dissimilar interface in the two series due to thermal agitation effects. XAS spectra at Fe and Co K-edges ensure similar local coordination of Co immaterial of stack order, contrary to altered local geometry of Fe observed in the two series ascribed to varied crystallinity of FePt. Such structures are useful for spin-wave assisted low field magnetization switching in highly coercive FePt by using exchange coupled soft FeCo.