Experimental Study Of Microwave Magnetic Properties Of Composites Under Magnetic Bias

The frequency dependencies of microwave permeability of composites filled with flake-shaped sendust (Fe-Al-Si alloy) powder particles are measured. A technique for determining the physical mechanisms resulting in the appearance of magnetic loss peaks is proposed. The technique consists in analysis of the data on microwave permeability obtained under external magnetic field. It is shown that the mixing rule, which correctly retrieves the intrinsic permeability in the absence of the external field, is not valid under magnetic bias. Based on the measured data, the physical mechanisms leading to the appearance of loss peaks are determined, and the invalidity of mixing rules under magnetic bias is explained. It is shown that the main peak of magnetic loss is attributed to the Polder-Smith modes. An increase in the external field leads to vanishing of the domain structure and to an increase in the interaction between powder particles. The permeability under bias should be described by mixing rules that take into account the interaction between inclusions. The found frequencies of the Polder-Smith modes are in good agreement with the permeability data.