Comparative Magnetic and Structural Properties Study of Micro- and Nanopowders of Nd2Fe14B Doped with Ni

Autor: G. A. Pérez Alcázar, J. S. Trujillo Hernandez, Jesús A. Tabares
Rok vydání: 2017
Předmět:
Zdroj: Journal of Superconductivity and Novel Magnetism
ISSN: 1557-1939
DOI: 10.1007/s10948-017-4086-5
Popis: Micropowders of melted and heat-treated Nd16(Fe76−x Ni x )B8 alloys system, with x = 0, 10, 20, and 25 (size distribution under 20 μm), were studied and compared with the study of nanopowders obtained, from the previous ones, by surfactant-assisted ball-milling process during 2 h. By XRD, a majority of Nd2Fe14B hard phase and a minority of α-Fe, Nd1.1Fe4B4 and NdNi2 phases were detected. The last one increases with Ni content. The crystallite size of the hard phase, in both types of samples, is not affected by the Ni content; however, the grains in micropowders are oblate, with a mean size of 37 nm, while those of the nanopowders are symmetric, with a mean size of 35 nm. Mossbauer spectra were fitted with seven sextets, which correspond to the six ferromagnetic sites of the hard phase and that of the α-Fe, and a doublet corresponding to the paramagnetic Nd1.1Fe4B4 phase. The mean hyperfine magnetic field, for both types of samples, decreases with Ni content. The hysteresis loops of both types of samples show a hard magnetic character, however, the coercive field and the M r/M s values for nanopowders are greater than those obtained for micropowders for all the Ni contents. Values of H c = 2 kOe and M r/ M s = 0.54 were obtained for nanopowders with 10 at.% Ni. From the hysteresis loops, which include the initial magnetization curve, Henkel plots for all the samples were obtained. These plots show that for micropowders, the predominant magnetic interaction is of dipolar type, while for nanopowders, the ferromagnetic exchange is the predominant one, which favored the magnetization.
Databáze: OpenAIRE
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