DISTRIBUTION OF NIOBIUM IN AN FE-PT-NB MAGNET

The role of Nb addition to improve the hard magnetic properties in FeP t magnet was investigated by characterizing microstructures of both Fe -39.5 at.%Pt binary and Fe-39.5 at.%Pt-0.75 at.%Nb ternary alloys usin gs transmission electron microscopy and atom probe field ion microscop y. In the as-quenched ternary alloy, the FePt ordered domains with a t weed contrast were observed as well as in the binary alloy. However, t he ordered domain size of the ternary alloy was slightly smaller than that of the binary alloy and comparable to the thickness of magnetic d omain wall. Although the coercivity of the as-quenched ternary alloy w as small, subsequent annealing produced high coercivity. Nb was rarely solved in the FePt ordered phase and was concentrated in spherical pa rticles of sub-microns in size. These particles may work as a pinning site against magnetic domain wall motion. Another possibility is that the change in composition ratio between Fe and Pt may be responsible t o the magnetic property change. (C) 1998 Elsevier Science S.A. All rig hts reserved.