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 ([mu] = [mu] - j[mu]') 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.sub.0.17][Zn.sub.0.22][Fe.sub.2.61][O.sub.4]) and #2 ([Ni.sub.0.19][Zn.sub.0.20][Co.sub.0.03][Fe.sub.2.58][O.sub.4]) by spin spray ferrite plating at 90[degrees]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.sub.dc] in the range of 1-3 GHz to give a similar spectrum to that of the film #2. The resonance field, [H.sub.R] of the film #2 under [H.sub.dc] of 1-2 kOe, which was strong enough to saturate the magnetization, exhibited a prominent in-plane angular dependence, while [H.sub.R] of the film #1 exhibited a very weak angular dependence. The difference between the maximum and the minimum values of [H.sub.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.sub.k] of about 60 Oe. Assigning [H.sub.k] of 60 Oe, we calculated the natural resonance frequency, [f.sub.r] as 1.6 GHz. This value approximately coincided with that of the higher frequency step of [mu]' 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. Index Terms--Complex permeability, ferrite plating, ferromagnetic resonance (FMR), Ni-Zn(-Co) ferrite film.