High Frequency Permeability of Thin Film Magnetic Core

The magnetization process of a thin film magnetic core at high frequencies was studied, using a simple magnetic closed circuit with a 17-turn coil. The permeabilities μ, μ ′ and μ ″ were measured. Below 5 MHz, μ and μ ″ increased with the coil current; this increase was inferred to be due to domain wall movement. Above 5 MHz, μ did not increase with the coil current, and it is assumed that domain wall movement does not occur readily above 5 MHz. The magnetic flux density in the core was calculated for frequencies 0.1 MHz~20 MHz, and was found to decrease with the frequency. Because domain walls do not move easily at high frequencies, it is expected that the flux in triangular domains at the edges of the core decreases with increasing frequency.