J. Phys. IV France 08 (1998) Pr2-95-Pr2-98
Magnetic properties of nanocrystalline CoFeNbB alloysL. Kraus1, V. Soyka1, P. Duhaj2 and Mat'ko2
1 Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 180 40 Prague 8, Czech Republic
2 Institute of Physics, Slovak Academy of Sciences, Bratislava, Slovakia, Dúbravská Cesta 9, 824 28 Bratislava, Slovakia
The influence of alloy composition and heat treatment on the structure and magnetic properties of rapidly quenched CoFeNbB alloys were studied. The saturation magnetization, Js, the magnetostriction constant. λs, and the Curie teniperature. Tc, of the as-quenched amorphous alloys decrease with increasing Nb or B content (3 < xNb < 7. 8 < xB < 15 at.%). Both Js, and λs, of CoFeNb7B9 show maxima at about 29 at.% of Co. The crystallization of all the alloys takes place in two steps. On the first step bcc-Fe(Co) grains develop in the amorphous matrix. With increasing Nb content their grain sizes substantially decrease. A nanocrystalline structure with the grain size of 10 - 15 nm is obtained for xNb = 7 at.%. The saturation magnetization increases on nanocrystallization. The magnetostriction constant, λs, is positive for the as-quenched as well as nanocrystalline alloys. Its magnitude first decreases and then remains constant or increases with further annealing. A slight decrease of the coercive field. Hc,, at the early stage of nanocrystallisation is followed by a subsequent gradual increase. The best soft magnetic properties were observed for the nanocrystalline Co25Fe59Nb7B9 alloy. The following parameters Js = 1.58 T. λs and Hc = 26 5 A/m. were obtained in this alloy after annealing at 600°C.
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