HIGH-FREQUENCY SOFT MAGNETIC PROPERTIES AND MAGNETIC DOMAIN STRUCTURES OF ULTRATHIN Co-BASED AMORPHOUS RIBBONS

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High-frequency magnetic properties of ultrathin Co-based amorphous ribbons fabricated in vacuum were studied and their domain patterns were observed by the Kerr effect. The samples used were zero magetostrictive ((Fe-Co)Cr_y)_x(Si-B)_<100-x'> (x=75-81), (y=0.05-0.06) amorphous alloys. The results obtained were as follows.(1) Extremely low core loss beyond 100 kHz was attained for the samples with a transverse field annealing. In the case of 6.0 mum thick ((Fe-Co)Cr_<0.06>)_<79>(Si-B)_<21> ribbon cores, the loss at 1 MHz for maximum flux density B_m=0.1T was 700 (mW/cc). This value was about 1/4 of that of Mn-Zn high-frequency ferrites or 5 mum Supermalloy tape wound cores.(2) Furthermore, marked improvements of frequency dependence of initial permeability were also obtained for ((Fe-Co)Cr_y)_x(Si-B)_<100-x'> (x=76-81) ribbons with transverse field annealing.(3) The domain patterns of some ultrathin ribbons were observed by the Kerr effect. The effect of transverse magnetic field annealing on the magnetic properties was also studied and their relation to the improvement of high-frequency properties was discussed.