The influence of Co on the magnetic properties of Fe–Si–B–Nb–Cu system

Abstract

With development of electric device with high running frequency and large power, classical Finemet alloys are not able to meet their requirements. In order to enhance its saturation magnetization, Fe79.5-xCoxSi6B12Cu1Nb1.5(x = 0, 5, 10 and 15) alloys with good amorphous forming ability had been designed. Furthermore, the strategy of optimizing annealing process was used to enhance the magnetic performance. Results show that when Co atoms entered into nanocrystalline grains in amorphous matrix, the saturation magnetization will enhance from 1.5T to 1.64T with the increase of Co content from 0 at. % to 5 at. %. The annealing temperature window can be widened by about 10K with increasing content of Co. The grain size for alloys with annealed at 823K for 5min is reduced from 40 nm of x = 0–31 nm of x = 5. After optimizing the annealing process, Fe74·5Co5Si6B12Cu1Nb1.5 shows very good saturation magnetization up to Ms = 1.64T, higher than Finemet classical system. Furthermore, the nucleation mechanism and grain growth are investigated to deeply understand the influences factors of magnetic properties. Kinetics of non-isothermal crystallization was also used to take a close look at the relationship between annealing temperature and grain size, which can guide future experiment or industrial production.