The effect of boron and rare earth contents on the magnetic properties of La and Cr substituted α-Fe/R2Fe14B-type nanocomposites

The effect of phase transformations on the magnetic properties of rare earth lean (Nd0.95La0.05)9.5Fe82.5−xCr2B6+x (x=0 to 4.5) and (Nd0.95La0.05)7.5+yFe80.5−yCr2B10 (y=0 to 4) melt spun ribbons has been investigated. The phase mixture, after optimum thermal processing, was found to be strongly dependent upon the rare earth and boron contents. Two magnetic phases, namely α-Fe and R2Fe14B, were found in (Nd0.95La0.05)9.5Fe82.5−xCr2B6+x alloy ribbons with x ranging from 0 to 4.5. For a fixed rare earth content, increases in the boron concentration resulted in a higher volume fraction of the R2Fe14B phase, which led to an increase in the intrinsic coercive force from 7.1 kOe for x=0 to 12.6 kOe for x=4.2. A Br=9.6 kG, iHc=9.5 kOe, and (BH)max=15.5 MGOe have been obtained in the alloy ribbons with x=4.5. On the other hand, the increase in the total rare earth content, or y, was found to suppress the formation of the metastable Fe3B and/or R2Fe23B3 phases and to yield an α-Fe/R2Fe14B mixture for y>1. This incr...