Improvement in high frequency magnetic properties of amorphous cores by thin surface oxide layers on ribbons

Abstract
A thin oxide layer with the effective thickness of about 150 nm was prepared on a surface of a thin Cobased amorphous ribbon by acid-treatmenl followed by annealing, and magnetic properties of cores made of it were studied. The oxide layers increased electric resistance between the ribbons and improved high frequency magnetic properties of the cores. For a core made of a 6.8-µm-thick ribbon, the acid-treatment increased the real part of the complex permeability, µ', by 60% and decreased tanδ/μ (δ : the loss angle) by 48% at 10MHz. The magnetic loss at a large excitation level was also reduced by the treatment. The obtained improvement was more remarkable than that obtained previously for the cores made of the ribbon with silicone interlayer insulation.