Improvement of size and magnetic properties of Nd9.5Fe72.5Ti3B15 bulk magnets by Zr or Nb substitution for Ti

Magnetic properties and microstructure of directly quenched Nd9.5Fe72.5Ti3-xMxB15 (M=Nb and Zr; x=0-3) bulk magnets in rod form with a diameter of 0.9 mm have been studied. Proper Nb or Zr substitution for Ti has been found to well modify phase constitution and to refine the grain size from 200 to 50-100 nm effectively. Accordingly, the magnetic properties of the rods are enhanced remarkably from H-i(c)=6.2 kOe and (BH)(max)=5.6 MG Oe for Nd9.5Fe72.5Ti3B15 to H-i(c)=6.7-15.4 kOe and (BH)(max)=6.0-8.2 MG Oe for Nd9.5Fe72.5Ti3-xMxB15. The optimum magnetic properties of B-r=6.6 kG, H-i(c)=9.6 kOe, and (BH)(max)=8.2 MG Oe can be achieved for Nd9.5Fe72.5Ti2.5Zr0.5B15 alloy, while the highest coercivity of H-i(c)=15.4 kOe [B-r=5.9 kG and (BH)(max)=7.0 MG Oe] is obtained for Nd9.5Fe72.5Nb3B15. Their high permanent magnetic property arises mainly from the existence of a large volume fraction of 2:14:1 phase, finer grain size, and the existence of grain boundary phase. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3068408]