Preparation of High‑Performance FeCoNi Thin Films by Magnetron Sputtering

This study explores the effects of sputtering pressure and power on FeCoNi high‑entropy alloy films prepared by DC magnetron sputtering, focusing on microstructure, surface morphology, and static/high‑frequency magnetic properties. In situ Lorentz TEM (LZ‑TEM) was used to directly observe magnetic domain evolution. Results show that low sputtering pressure (1 mTorr) promotes strong FCC (111) crystallization, smooth and dense surfaces. Increasing pressure leads to amorphization, higher roughness, and degraded magnetic performance. Under optimized pressure, 100 W sputtering power yields the best crystallinity, smoothest surface, and optimal soft magnetic properties, including high remanence ratio, low coercivity, and clear ferromagnetic resonance in the 2–7.5 GHz range. The optimal parameters are confirmed as 1 mTorr and 100 W, producing uniform nanocrystalline FeCoNi films. In situ LZ‑TEM reveals river‑like domain walls, vortex–antivortex structures, and uniform magnetic moment precession, indicating weak domain pinning and excellent high‑frequency magnetization consistency. This study provides experimental and theoretical support for the controllable fabrication of high‑performance FeCoNi soft magnetic films for high‑frequency devices.