Discussion of strong pinning effect via nonuniform PSSW mode in Fe/NiFe/Fe multi-layer films with different Fe film thicknesses

Abstract Multilayer films with high saturation magnetization and low ferromagnetic resonance linewidth have great potential for various applications in the era of high frequency and miniaturization. In this study, Fe (t nm)/Ni81Fe19 (50 nm)/Fe (t nm) multilayer films were fabricated using electron beam evaporation, and the microstructure, saturation magnetization, coercivity, ferromagnetic resonance (FMR) linewidth and perpendicular standing spin-wave (PSSW) mode are discussed in detail. With increasing Fe film thickness, the saturation magnetization of the multilayer films increased from 10,547 to 14,494 Gs, becoming closer to the theoretical value, and the ferromagnetic resonance linewidth showed an overall increasing trend. It is worth noting that a strong pinning effect has been found via the appearance of the PSSW mode in the FMR spectrum, when the thickness of Fe reaches 4 nm. As the thickness of the Fe film increased from 4 to 15 nm, the perpendicular standing spin-wave field (Hp) increased from 133 to 379 Oe, and the perpendicular standing spin-wave linewidth (ΔHp) increased from 68 to 148 Oe. Remarkably, with 8 nm thick Fe film, the multilayer films achieved excellent comprehensive performances with high saturation magnetization (4πMs, 13,525 Gs), a low in-plane ferromagnetic resonance field (Hr, 725 Oe), and a low FMR linewidth (ΔH, 84.24 Oe).