Magnetic and structural properties of amorphous and nanocrystalline FeNi-based alloys

Abstract

Nanocrystalline soft magnetic ribbons, with a composition of (Ni/sub 0.78/Fe/sub 0.22/)/sub 89-x/Zr/sub 7/B/sub 4/Cu/sub x/ (where x is 0 or 1), were synthesized by melt spinning and subsequent crystallization. The best magnetic properties coincided with the development of a single nanocrystalline phase at annealing temperatures just above the primary crystallization. Differential thermal analysis indicates a 60/spl deg/C difference between primary and secondary crystallization temperatures. This makes the nanocrystallization process for these materials more difficult than similar alloy systems. The alloy containing Cu exhibited good soft magnetic properties after annealing at 550/spl deg/C for one hour. X-ray diffraction indicated a face-centered cubic phase with an average grain diameter of 8 nm, and vibrating sample magnetometry indicated a coercivity of 13 Oe and a normalized magnetic moment of 71 emu/g. The alloy without Cu showed improved properties for an annealing temperature of 475/spl deg/C. A small value of 3.7 ppm for the saturation magnetostrictive coefficient was measured in the optimally annealed Fe/sub 19.36/Ni/sub 68.64/Zr/sub 7/B/sub 4/Cu/sub 1/ alloy.