Achieving high energy products in anisotropic Nd-Fe-B/Fe composite thick films by Dy co-sputtering

To realize a high magnetization while ensuring a high coercivity in Nd-Fe-B/Fe composite thick films, this work proposes a spatially selective Dy co-sputtering strategy that precisely introduces Dy into surface and interfacial regions. This approach significantly strengthens the magnetocrystalline anisotropy and columnar grain continuity, yielding a coercivity of 1.75 T, a remanence of 1.23 T, and a maximum energy product of 35.2 MGOe. Microstructural analyses reveal that the Dy co-sputtering not only adjusts the local chemical composition to form (Nd,Dy)₂Fe₁₄B with a high magnetocrystalline anisotropy but also induces a microstructural reconstruction, leading to a synergistic enhancement of both coercivity and remanent magnetization. The first-order reversal curve and magnetic domain observations demonstrate that the long-range dipole interaction between the soft- and hard-magnetic layers is enhanced, which shifts the magnetization reversal mechanism from nucleation-dominated to pinning-dominated, evidencing a pronounced magnetic hardening effect. These findings establish that Dy-assisted microstructure optimization and magnetic hardening, together with the high magnetization provided by the Fe soft-magnetic layer, offer an effective pathway for fabricating high-performance Nd-Fe-B/Fe composite thick films being compatible with micro-electromechanical systems.