High-Frequency Soft Magnetic Properties of Co–SiO2 Nanogranular Films With Large Out-of-Plane Magnetic Anisotropy

For their use as flexible frameworks in high-frequency electromagnetic devices, soft magnetic thin films must have a high relative permeability μ up to frequencies of the order of 10 GHz and must overcome directional limitations. In this study, we demonstrate full in-plane, high-frequency, soft magnetic performance of Co
_x
-(SiO
₂
)
_1-x
nanogranular films with large out-of-plane anisotropy. For a film with Co concentration x = 0.52, we obtained a high value μ = 4 up to the resonance frequency of 13 GHz for every direction in the film plane. The fine magnetic-maze-domain structure that we observed using magnetic force microscopy was unaffected by the application of an external magnetic field. Both the large out-of-plane anisotropy fields of a few thousand oersteds and the negligibly small remanent magnetization contribute to produce a resonance frequency greater than 10 GHz and to enable magnetically isotropic conditions in the film plane, with high reversibility in external magnetic fields. This film with the large out-of-plane anisotropy promises to be a useful material for applications in fully directional and flexible designs of electromagnetic devices.