Experimental determination of magnetocrystalline anisotropy constants and saturation magnetostriction constants of NiZn and NiZnCo ferrites intended to be used for antennas miniaturization

摘要

This study investigates the magnetocrystalline anisotropy constants (K_1) and the saturation magnetostriction constants (λ_S) of Ni_(1-x)Zn_xFe_2O_4 (NiZn) and Ni_(0.8-x)Zn_xCo_(0.2)Fe_(1.98)O_(4-δ) (NiZnCo) ferrites intended to be used for antenna downsizing. Composite materials constituted of soft ferrite nanosized particles (NiZn or NiZnCo ferrites) embedded in an epoxy matrix are realized. Measurements of their magnetic permeability in the frequency range of 200 MHz-6 GHz are performed. The influence of compressive stress (in the range of 32-96 MPa) on their Ferrimagnetic Resonance (FMR) is demonstrated. An analytical modeling of stress-induced FMR changes is proposed that allows simultaneous determinations of the Natural Ferrimagnetic Resonance (NFMR, F_0), K_1 and λ_S of Ni_(1-x)Zn_xFe_2O_4 and Ni_(0.8-x)Zn_xCo_(0.2)Fe_(1.98)O_(4-δ) ferrites. The obtained results for NiZn ferrites are in agreement with literature data, validating both the experimental process and the proposed modeling of the stress-induced FMR changes. Regarding NiZnCo ferrites, extended data on K_1 and λ_S are presented for the first time. Increasing zinc content (x) induces a spin disorder that reduces in a same time K_1 and the magnetization at saturation M_S. The rapid variation of K_1(x) is related to that of the magnetization M_S(x) through a power law. The single-ion anisotropy model allows a satisfactory interpretation of K_1 dependence on zinc content. The unexpected low values of λ_S got for NiZnCo ferrites, compared to those got for NiZn ferrites, are also discussed. Application of compressive stress lowers noticeably magnetic losses of Ni_(0.6)Zn_(0.2)Co_(0.2)Fe_(1.98)O_(4-δ) at given frequency, thereby enhancing the ability of this spinel ferrite to be used as a substrate in the aim of antenna miniaturization.