Magnetic properties of B-rich nanocomposite REy(TM)90-y-xMxB10 (RE=Nd+Pr, TM=Fe, Fe+Co, M=Nb, Ta, y=8,10, x=0-4) alloys

摘要

Nanograined hard magnetic rare earth (R)-iron-boron-based alloys have attracted considerable scientific and technological interest over the past 15 years [1,2]. The reason for the intense interest is the exchange enhancement of the remanence Jr and maximum energy density (BH)max that occurs when the mean crystallite size for the R2Fe14B phase in melt spun alloys is reduced below about 50nm and by introducing a soft magnetic second phase, to yield a nanocomposite magnet [3,4]. For this coupling to be effective, the corresponding soft/hard mean grain sizes should ideally be of 10nm for the soft phase and 20nm for the hard phase, according to numerical simulations, in order to avoid independent magnetization reversal at the soft grains [5]. Additional features of these alloys are moderate intrinsic coercivity iHc values (within the range 250-500kA/m, depending on composition) together with lower raw material cost due to reduced rare-earth content, which represent a useful advantage for commercial purposes.