Investigation of the gyromagnetic permeability of amorphous CoFeNiMoSiB manufactured by different techniques

The permeability of amorphous non-magnetostrictive flexible ferromagnetic films is investigated in the 10 MHz to 1.6 GHz range. The permeability of melt-spun ribbons is shown to increase after chemical thinning, but no improvement is seen concerning losses in this frequency range. It is shown that demagnetizing fields affect the measured permeability, either because of finite sample size effects, or because of thickness inhomogeneities. Thinner layers were manufactured by ion beam sputtering using the melt spun ribbons as targets. Real permeability levels of 500 and resonance frequencies close to 1 GHz are observed on the layers sputtered on Kapton as well as on that sputtered on glass substrates. After annealing, flexible material with initial permeability higher than 1500 and resonance frequency of 530 MHz is produced. The study of the permeability on a broad frequency range indicates that the occurrence of high frequency losses in the hundred MHz range is-due not to skin effect but to intrinsic damping of the gyromagnetic resonance.