PHASE SEGREGATION AND INTERACTIONS IN DY-SUBTITUTED MELT-SPUN ND-FE-BALLOYS

We have analyzed in this work the effects of the partial and total sub stitution of Nd by Dy in melt spun Nd15Fe76B9 alloys prepared by cryst allization of amorphous precursors. Depending on the crystallization p arameters, and particularly on the heating rate employed in order to r each the annealing temperature, samples with either one or two reversa l steps in the demagnetization curve may be produced. The temperature of spin reorientation (SRT), measured by two different methods, was sh own to be independent of the composition, close to 110K, for samples w ith a Dy content between 20% and 80% of the total rare earth. This led us to suggest that, two different hard phases with low Dy and Nd cont ent, respectively, are present in the samples. The existence of either one or two reversal steps, depending on the heating rate employed, st rongly supports the existence of exchange-driven collective demagnetiz ation processes.