The effect of ambient chamber pressure on the magnetic properties and surface morphology of nanocrystalline PrFeB melt spun ribbons

The magnetic properties of REFeB melt spun permanent magnetic alloys is highly dependent upon the grain size of the melt spun ribbon produced. The entrapment of gas pockets between the melt and the roll causes areas of locally lower cooling rates and these regions have substantially coarser grains which causes the magnetic properties to become less uniform. The present paper reports an investigation of the effect of reducing the ambient chamber pressure, with the particular aim of determining the threshold pressure for the avoidance of the gas pockets when spinning a nanophase alloy in argon. A PrFeB alloy of stoichiometric composition was studied for various chamber pressures, from 1.0 atm down to 0.25 atm, and it was found that the most marked reduction in the gas pockets accompanied by improvements in remanence and energy product occurred in the pressure range 0.6 to 0.5 atm. (orig.)