Change in High Frequency Magnetic Properties with Isothermal Annealing in Amorphous Ferromagnetic Fe<SUB>80</SUB>P<SUB>13</SUB>C<SUB>7</SUB> and Fe<SUB>75</SUB>Si<SUB>15</SUB>B<SUB>10</SUB> Alloys

Effects of isothermal annealing (200∼470°C, 30∼420 min) on permeability and core loss in the frequency range between 0.5 and 200 kHz have been studied for rapidly quenched amorphous Fe80P13C7 and Fe75Si15B10 alloys. The results obtained are summarized as follows:(1) μ′ vs H curves measured show two maxima above 0.5 kHz in the as-prepared samples, and above several kHz in the annealed samples.(2) Permeabilities measured at H=4 A/m, f=1 kHz in the as-prepared Fe80P13C7 and Fe75Si15B10 samples are (0.4∼1)×4π×10−4 H/m and (0.7∼1.5)×4π×10−4 H/m, respectively.(3) Core losses measured at Bm=0.1 T, f=1 kHz in the as-prepared Fe80P13C7 and Fe75Si15B10 samples are 3∼6 J/m3 and 4∼6 J/m3, respectively.(4) The optimum annealing condition to improve initial permeability and to decrease a core loss is annealing at 300∼350°C for Fe80P13C7 alloy and at 400∼470°C for Fe75Si15B10 alloy for several tens of min.(5) After annealing in the above condition, μ′(4 A/m) increases 3∼4 times and the core loss decreases to approximately one-half those of the as-prepared samples for both alloys.On the assumption that soft and hard magnetic regions exist in the as-prepared amorphous samples, the two maxima in μ′ vs H curve and also the anomaly in lnW vs lnBm can be explained.About 85∼90% of the core loss measured is the eddy current loss. If we assume that the number of domain wall increases with increasing the frequency, the frequency dependence of eddy current loss can be explained by the plane wall model proposed by Pry and Bean.