Effect of longitudinal magnetic field annealing process on the properties and structures of soft magnetic Fe73.7Si15.3Cu1Nb3B7 nanocrystalline alloys

Fe73.7Si15.3Cu1Nb3B7 nanocrystalline alloy was subjected to longitudinal magnetic field (LMF) annealing treatment, and the influence of different magnetic field strengths (MFS) on the magnetic properties and microstructure of the nanocrystalline soft magnetic alloy was investigated. The results showed that the Hc and Pv of nanocrystalline magnetic rings tended to increase and then decrease with increasing MFS, on top of that reached the minimum value at the MFS of 0.59 mT, which was 0.51 A/m and 89.86 W/kg (test conditions: Bm = 0.4 T, f = 50 kHz), respectively. The μe is the highest value in the same test frequency range of 10–1000 kHz. Besides, the rectangular ratios of the magnetic rings were all above 0.95 when the applied MFS was higher than 0.24 mT. The formation of lamellar domains inside the alloy after LMF annealing was observed by the magneto-optical Kerr effect, with the MFS increasing, the direction of the domains gradually parallel to the strip direction, and the width of the domain walls increasing all the time. The optimum soft magnetic performance of the strip was achieved when the angle between the magnetic domains and the easy magnetization direction was 21.9°.