Isotropic nanocomposite Pr–Fe–Co–B ribbons with (BH)max>20MGOe

We have studied the effect of wheel speed and ejection temperature on the magnetic properties and microstructure of melt-spun Pr9Fe80Co5B6 ribbons. The results obtained indicate a strong dependence of the microstructure and magnetic hardness on the melt temperature at ejection. The thickness of the optimum ribbons was found to be in the range of 36–40μm. The as-made ribbon samples were found to be crystalline at an ejection temperature between 1300–1400∘C. The ribbons become amorphous at a higher ejection temperature (above 1500∘C). The ejection temperature for the best sample was 1360∘C. At this temperature the maximum energy product obtained was 21 MGOe associated with a coercivity of 6.3 kOe for a wheel speed of 18 m/s. Microstructure studies on the optimum samples show a uniform distribution of magnetically hard 2:14:1 and soft αα-Fe phases with a grain size of about 20 nm. The enhanced magnetic properties are attributed to an optimum inter-grain exchange coupling between the magnetic moments of the hard and soft grains in the sample with finer microstructure.