The influence of ambient gas pressure on the surface quality and magnetic properties of nanocrystalline NdFeB based melt spun ribbons

The melt spinning of a NdFeB alloy of stoichiometric composition was investigated under various ambient gas pressures, from atmospheric pressure, 100 kPa (760 Torr) to vacuum, 0.13 Pa (10-3 Torr). Gas pockets were observed on the roll contact surface of ribbons produced at pressures close to atmospheric, whilst a reduction in pressure, to 50 kPa (380 Torr) caused the disappearance of the gas pockets. The absence of the gas pockets led to more consistent magnetic properties for the nanocrystalline ribbon.