Soft magnetic properties of ultrathin Co-based amorphous alloy ribbons with thickness of 3-10 μm

Ultrathin zero-magnetostrictive amorphous ((Fe_0.05Co _0.95)_0.95 Cr_0.05)₇₅(Si_0.5B_0.5)₂₅ ribbons with thickness of 3-10 μm were fabricated by a single roller quenching method in vacuum. The ribbons obtained had a good smooth surface and dimensional uniformity. The core loss of toroidal samples 10 mm in diameter was measured after annealing and found to decrease with decreasing ribbon thickness. For 5.5-μm-thick ribbons, the losses at 1 MHz and 10 MHz were 1.0 J/m³ (=1.0 W/cm³ ) and 8.8 J/m³ (=88 W/cm³) for B _m=0.1 T, respectively. The former value was 2/5 that of Mn-Zn high-frequency ferrites and 1/3 that of 5-μm Supermalloy tape wound cores. Furthermore, extremely low losses were obtained for 3.8-μm-thick ribbon at 2-10 MHz. In addition, remarkably high initial permeability beyond 100 kHz was also attained. The values of 5.5-μm-thick ribbons measured at 1 and 10 MHz were about 10000 and 1200 for H_m=2 mOe, respectively