Magnetic properties and microstructure of directly quenched Nd9.5Fe75.5-xMxB15 (M=Mo, Nb, Ta, Ti, V, and Zr; x=0-4) bulk magnets

Magnetic properties and microstructure of directly quenched Nd9.5Fe75.5-xMxB15 (M=Mo, Nb, Ta, Ti, V, and Zr; x=0-4) bulk magnets in rod form with a diameter of 0.7 mm have been studied. The substitution of the selected refractory elements for Fe in the Nd9.5Fe75.5MxB15 alloy can suppress the formation of the soft phases, including Nd2Fe23B3 and one unknown phase, leading to the presence of a large amount of the Nd2Fe14B phase. Besides, the grain size at the core side of the rods is refined from a micrometer scale for a ternary magnet to 50-120 nm for the magnets with refractory element substitution. As a result, the magnetic properties are improved remarkably from B-r=5.0 kG, H-i(c)=1.0 kOe, and (BH)(max)=1.7 MG Oe for a ternary magnet to B-r=5.7-6.5 kG, H-i(c)=2.0-14.6 kOe, and (BH)(max)=3.1-8.7 MG Oe for refractory element substituted magnets. The optimal magnetic properties of B-r=6.5 kG, H-i(c)=10.3 kOe, and (BH)(max)=8.7 MG Oe can be achieved in the Nd9.5Fe72.5Ti3B15 magnet, while the highest coercivity of H-i(c)=14.6 kOe, with B-r=5.9 kG and (BH)(max)=7.4 MG Oe, is obtained in the Nd9.5Fe71.5Nb4B15 magnet. (C) 2008 American Institute of Physics.