Papers by Keyword: Nanocomposite Magnet

Abstract: In this study, the particle sizes of SrFe₁₂O₁₉ in hard/soft SrFe₁₂O₁₉/CoFe₂O₄ nanocomposite magnets made using mechanical alloying and ultrasonic irradiation were investigated. SrFe₁₂O₁₉/CoFe₂O₄ nanocomposites were combined in a ratio of 75:25, with each magnetic material being prepared separately. SrFe₁₂O₁₉ powder was prepared from Fe₂O₃ and SrCO₃ powder by mechanical alloying and ultrasonic irradiation for different times, 0, 3, 6, 9, and 12 h. Varying the ultrasonic time during the preparation of the SrFe₁₂O₁₉ samples resulted in differences in morphological characteristics, crystal structure, particle size, crystal size, microstrain, density, porosity, and magnetic properties. The longer the ultrasonic time, the crystal size and particle size decreases, the density increases, and the porosity reduction which affects the magnetic properties. SrFe₁₂O₁₉ after 12 h ultrasonic process reach M_s value = 61.29 emu/g. CoFe₂O₄ powder was produced from Fe₂O₃ and CoCO₃ powder by mechanical alloying with a 10 h milling time. Furthermore, each SrFe₁₂O₁₉ sample was composited with CoFe₂O₄ powder by ultrasonic irradiation for 1 h and these composite samples also showed different characteristics, where there is an increase in M_r and M_s compared to the single SrFe₁₂O₁₉. The morphology, crystal structure, particle size, and magnetic properties of the samples were measured using scanning electron microscopy, X-ray diffraction, particle size analysis, and PERMAGRAPH. The crystal size and microstrain were calculated using a Williamson–Hall plot, and density and porosity were determined using Archimedes’ law.

Abstract: The pulse-laser-crystallization (PLC) technique was applied to Nd3.7Pr3.4Dy0.9Fe86B5Nb1 amorphous ribbons. After irradiation with a 248nm KrF pulse excimer laser at a fequency of 15Hz for 1 min, the Nd3.7Pr3.4Dy0.9Fe86B5Nb1 amorphous ribbons crystallized into the homogeneous Nd2Fe14B/α-Fe nanocomposite permanent magnetic materials with an average grain size around 26nm. The obtained coercivity, remanence, and (BH)max values were 6.6 K, 1.23 T, and 18.5 MGOe, respectively.

Abstract: In Nd9.5Fe84B6.5 melt-spun ribbon, the quenching temperature is found to be effective for the texture development of Nd2Fe14B nanocrystals. For a relatively low quenching temperature of 1250°C a (00l) texture of Nd2Fe14B crystals was found on the free-side surface of the ribbons. At a higher quenching temperature of 1350°C, the microstructure of the free-side surface of the ribbons switches into (320) and (517) texture. It is believed that the transformation of the melt at higher temperature triggers the switch of the texture.

Abstract: A physically-based model is proposed for the competitive precipitation of multiple phases (bcc-Fe, Fe3B, Nd2Fe14B, Nd2Fe23B3, NdFe4B4 and Fe2B) from an amorphous Fe-B-Nd matrix. These materials form the basis of a class of nanocomposite hard magnets. The nucleation and growth of the different phases are calculated using computational thermodynamics and kinetics tools with input from a thermodynamic assessment of this system. In some alloy compositions, the phase formation sequence during crystallization shows significant sensitivity to the heating-rate. Model calculations illustrate that this effect cannot be explained by homogeneous nucleation and growth of the phases. The possible role of heterogeneous nucleation is briefly discussed.