This work demonstrates the dependence between magnetic properties and the thickness of NiFe thin films. More importantly, a quantitative study of the surface composition of NiFe thin film exposed to atmospheric conditions has been carried out employing angle-resolved X-ray photoelectron spectroscopy (ARXPS). In this study, we fabricated Ni₈₁Fe₁₉ (NiFe) thin films on Si (100) substrate using electron beam evaporation and investigated their surface morphologies, magnetic properties, and the thickness of the surface oxide layer. The coexistence of metallic and oxidized species on the surface are suggested by the depth profile of ARXPS spectra. The thickness of the oxidized species, including NiO, Ni(OH)₂, Fe₂O₃, and Fe₃O₄, are also estimated based on the ARXPS results. This work provides an effective approach to clarify the surface composition, as well as the thickness of the oxide layer of the thin films.

Excellent gyromagnetic properties of textured, bulk Ba-hexaferrite samples are required for low-loss, self-biased applications for microwave and millimeter-wave (MMW) devices. However, conventionally processed bulk Ba-hexaferrite ceramics typically demonstrate low remanent magnetization values, 4πM_r, of 2.0~3.0 kG, and relatively large ferromagnetic resonance (FMR) linewidths, ΔH_FMR, of 0.8~2 kOe. These properties lead to the development of high-performance, practical devices. Herein, crystallographically textured Ba-hexaferrite samples, of the composition Ba_0.8La_0.2Fe_11.8Cu_0.2O₁₉, having excellent functional properties, are proposed. These materials exhibit strong anisotropy fields, H_a, of ~14.6 kOe, high remanent magnetization, 4πM_r, of 3.96 kGs, and a low ΔH_FMR of 401 Oe at zero-bias field at the Q-band. Concomitantly, the broadband millimeter-wave transmittance was utilized to determine the complex permeability, μ*, and permittivity, ε*, of textured hexaferrites. Based on Schlöemann’s theory of complex permeability, μ*, the remanent magnetization, 4πM_r, anisotropy field, H_a, and effective linewidth, ΔH_eff, were estimated; these values agree well with measured values.

A simple and convenient method is demonstrated in this work by continuously applying uniaxial tensile strains to tune the high-frequency properties of flexible magnetic films. The magnetostriction effect causes the uniaxial magnetic anisotropy in the Ti/Fe/Ni₈₁Fe₁₉/Fe/Ti multilayer film when the flexible substrate transitions from the convex state to the planar state after preparation. In addition, the microstructure, magnetic domain morphology, and the high-frequency magnetic performance of the pre-strained Ti/Fe/Ni₈₁Fe₁₉/Fe/Ti multilayer films are investigated. The results show that the flexible Ti/Fe/Ni₈₁Fe₁₉/Fe/Ti multilayer films’ initial permeability can be monotonically varied over a hundred units, and the resonant frequency can be adjusted around 1.5 GHz. The flexible Ti/Fe/Ni₈₁Fe₁₉/Fe/Ti films, with their elastic-tunable magnetic performance, are promising candidate materials for flexible microwave devices.