Nanocomposite hard magnetic materials (Nd,Dy)_4.5Fe _77.5B₁₈ (No. 1) and (Nd,Dy)_4.5Fe ₇₆B₁₈Nb_1.2Cu_0.3 (No. 2) have been prepared by crystallizing amorphous ribbons, fabricated by single roll melt-spinning. The evolution of a multiphase structure was monitored by an x-ray diffractometer and by thermomagnetic measurement. We observed that, at annealing temperatures below 670 °C, there is crystallization of soft phase Fe₃B and a small amount of hard phase Nd₂Fe₁₄B. At annealing temperatures above 670 °C, crystallization of α-Fe and probably Dy₂Fe₁₄B phases with large magnetocrystalline anisotropy led to a drastic enhancement in the hard magnetic properties of the materials. The maximum value of H_C is found to be 4.2 kOe for sample No. 1. For sample No. 2, with co-doping of Nb and Cu, nanostructure refinement yields a strong enhancement in exchange coupling between the component phases. Thereby, we obtained high reduced-remanence of 0.78, high remanence of 1.15 and a high (BH)_max value up to 16.2 MGOe. © 2007 IOP Publishing Ltd.

The N.D., Hoa N.Q., Oh S.K., Yu S.C., Anh H.D., Vu L.V., Chau N.

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Từ khóa : Annealing; Coercive force; Doping (additives); Dysprosium; Magnetocrystalline anisotropy; Nanocrystallization; Remanence; X ray diffraction analysis; Multiphase structure; Nanocomposite magnets; Thermomagnetic measurement; Magnets