Engineering Interfacial Perpendicular Magnetic Anisotropy in Fe2CoSi/Pt Multilayers with Interfacial Strain and Orbital Hybridization

We report a large interfacial perpendicular magnetic anisotropy (PMA) in [Fe2CoSi/Pt]n (FCS/Pt) multilayers deposited on thermally oxidized Si substrates. A maximum anisotropy energy density, Ku, of 2.64 Merg/cm3 is achieved with an optimized stack. We are able to tune the PMA by adjusting the Pt and FCS film thicknesses and number of periods of the multilayer structure, as these significantly affect the lattice structure of FCS/Pt stack. Both high-resolution transmission electron microscopy and structural relaxation of the atomistic model using first-principles calculations reveal that while the multilayer structure assumes a monoclinic structure (α = 84°), the FCS films undergo a local orthorhombic distortion from the bulk structure due to the strain imposed by the FCS/Pt interface. By analyzing the orbital-resolved density of states of the system, we propose that both the orthorhombic distortion of the FCS and orbital interactions between interface Pt and Fe atoms are responsible for the high PMA. For the first time, a large interfacial PMA is demonstrated in the Fe-based Heusler/Pt multilayer structure with underlying mechanisms discussed via both experiments and first-principles calculations. Thus, we have shown that there is great potential in strain-enhanced FCS/Pt multilayers in future applications in spintronic devices.