Phase segregation and interactions in Dy-substituted melt spun Nd-Fe-B alloys

We have analyzed in this work the effects of the partial and total substitution of Nd by Dy in melt spun Nd/sub 15/Fe/sub 76/B/sub 9/ alloys prepared by crystallization of amorphous precursors. Depending on the crystallization parameters, and particularly on the heating rate employed in order to reach the annealing temperature, samples with either one or two reversal steps in the demagnetization curve may be produced. The temperature of spin reorientation (SRT), measured by two different methods, was shown to be independent of the composition, close to 110 K, for samples with 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 content, respectively, are present in the samples. The existence of either one or two reversal steps, depending on the heating rate employed, strongly supports the existence of exchange-driven collective demagnetization processes.