Magnetic Properties of Soft Magnetic Powder/Epoxy Composite Sheet

This article describes the development of a composite resin magnetic sheet of soft magnetic powder and epoxy resin used in the beyond 10 MHz band magnetic devices. Magnetic powder and epoxy resin were mixed, dispersed, and formed into a sheet shape by the bar coating method. Fe–Si-based polycrystalline fine powder, Fe–Si–Cr-based amorphous fine powder, and Fe–Si–Nb–Cu–B-based nanocrystalline fine powder with an average particle were used as the starting soft magnetic powder. In addition, submicrometer Fe–Si–Cr-based powder was used to further increase the packing density of the magnetic powder in the composite sheet. In the evaluation of the magnetic sheet, saturation magnetization, coercivity, relative magnetic permeability, and loss-tangent in the range from 10 MHz to hundreds of MHz were measured. A magnetic sheet using the nanocrystalline powder and submicrometer powder showed a high relative permeability of 13 and a low loss-tangent of 0.05 at 100 MHz.