Effects of two-step annealing on the microstructures and soft magnetic properties of nanocrystalline Fe86Zr7B6Cu1 ribbons

The effects of two-step annealing on the microstructures and soft magnetic properties of nanocrystalline Fe86Zr7B6Cu1 ribbons were studied. Two-step annealing results in a marked decrease of grain size and a distinct improvement of soft magnetic properties with respect to conventional annealing at 600°C for 1h. Bcc α-Fe with the grain size of 8nm is formed in ribbon after it is pre-annealed at 750°C for 2min followed by annealing at 600°C for 58min. Its coercive force Hc, initial permeability μi, and relaxation frequency f0 are 1.5A/m, 6.15×104, and 8.9×104Hz, respectively. The decrease of grain size may result from a larger value of the nucleation rate obtained during the initial stage of crystallization by annealing amorphous ribbon at higher temperatures for short duration. But pre-annealing at 800°C leads to the decrease of soft magnetic properties because of the formation of Fe3Zr.