Effect of La-substitution on microstructure and magnetic property of melt-spun (Nd1−xLax)13Fe81B6 alloys

The expensive rare earth elements Nd, Pr, Dy and Tb have been extensively used for making NdFeB-based magnets, but the less expensive and high abundant rare earth (HARE) elements such as La and Ce have been over stocked. The marketing expansion of the HARE elements is of much interest in academia and industry to achieve effective and efficient utilization of HARE elements. In this paper, nanocrystalline (Nd1−xLax)13Fe81B6 (x = 0-0.5) alloys were fabricated by melt-spinning method. It is found out that the room temperature magnetic properties of the alloys decrease sharply when La is substituted for Nd up to 20 at.%. However, an anomalous increase in Jr value and improved thermal stability of the alloy ribbons are observed for 40 at.% La substituted alloy while the reduction in magnetic properties is only nominal up to 30 at.%. Furthermore, the Curie temperature decreases from 588 K to 561 K with 50 at.% La substitution, which is higher than the equal amount of Ce substitution in Nd-Fe-B. It is shown by the Henkel curves that the alloy with 40 at.% La has the biggest value of positive peak which demonstrates the strongest exchange coupling in the 40 at.% La substituted alloy. The TEM micrographs indicate that the alloy containing 40 at.% La has more uniform and refined microstructure resulted in the enhanced properties.