Dependence of dynamic losses on the thickness of rapidly solidified FeSi6.5 ribbons

The total and the dynamic magnetisation loss of annealed FeSi6.5 ribbons versus thickness show minima at values in the range of 40–100 μm depending on magnetisation frequency and polarisation. At constant frequency and polarisation the anomaly factor as a function of the ribbon thickness in a logarithmic plot can be divided into two linear regions with different slopes. For thick ribbons the anomaly factor is reciprocal to the thickness and for thin ribbons it is reciprocal to the cube of the thickness. The annealed FeSi6.5 ribbons have a 100〈011〉 texture where the (100) pole is tilted against the surface normal of the ribbons by about 17 °. This leads to closure domains reducing the magnetostatic energy. A model considering lower mobility of the domain walls at the surface of the ribbon describes well the found dependency of the anomaly factor on the ribbon thickness. The depth of the according surface layers can be estimated to be about 15 μm.