FMR study on spin-sprayed Ni-Zn-Co ferrite films with high permeability usable for GHz noise suppressors

We previously revealed that spin sprayed Ni-Zn ferrite films had a weak in-plane uniaxial magnetic anisotropy induced parallel to the liquid flow direction during the spin spraying. Adding a small amount of Co to the films, we made the uniaxial magnetic anisotropy definitely strong. The imaginary part of the complex permeability (μ=μ´-jμ´´) of the Co-containing films measured in the remanence state exhibited a dual step-like dispersion. In order to reveal the influence of magnetic anisotropy of the films on the magnetic resonance, we deposited, in this study, films #1 (Ni_0.17Zn_0.22Fe_2.61O₄) and #2 (Ni_0.19Zn_0.20Co_0.03Fe_2.58O₄) by spin spray ferrite plating at 90°C. The imaginary permeability in the remanence state of the film #1 (which exhibited no definite in-plane magnetic anisotropy) had a maximum at about 450 MHz, which increased with increasing external dc magnetic field, H_dc in the range of 1-3 GHz to give a similar spectrum to that of the film #2. The resonance field, H_R of the film #2 under H_dc of 1-2 kOe, which was strong enough to saturate the magnetization, exhibited a prominent in-plane angular dependence, while H_R of the film #1 exhibited a very weak angular dependence. The difference between the maximum and the minimum values of H_R for the film #2 was about 60 Oe. This means that the film #2 consists of two regions, one with a crystalline anisotropy field having an in-plane isotropic distribution due to the cubic spinel structure, and the other with an induced uniaxial anisotropy field, H_k of about 60 Oe. Assigning H_k of 60 Oe, we calculated the natural resonance frequency, f_r as 1.6 GHz. This value approximately coincided with that of the higher frequency step of μ´´ for the film #2 in the remanence state. This suggests that the magnetic loss in the remanence state for the films like #2 (which exhibit prominent uniaxial anisotropy induced in film plane) is ascribed to the two regions described above.