Analysis of eddy current loss in Mn–Zn ferrites for power supplies

From the investigation regarding the dependence of power loss and electrical resistivity at a temperature at which crystalline anisotropic energy becomes zero, eddy current loss and residual loss could be obtained separately. The increase in residual loss as exciting magnetic flux density, Bm, follows Bm2 at 1 MHz and Bm3–4 at 100 kHz. This result shows that the residual loss arises from spin rotation inside the magnetic domain wall. The domain size was estimated to be in the region of 1–2 μm by applying the barlike domain-wall model to the eddy current loss obtained experimentally. The frequency of the spin rotation is estimated using the domain size, the thickness of the domain wall, and the exciting condition. The spin rotation inside the domain wall can reach the magnetic resonant frequency of Mn–Zn ferrites under the exciting condition of f>500 kHz and Bm>70 mT. This magnetic resonance occurring inside the domain wall is considered to generate the large residual loss.