Exchange Coupling in MnAlC/α-Fe Nanocomposite Magnets
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Nanostructured composite materials consisting of exchange-coupled hard and soft magnetic phases are proposed as alternative for the development of high-energy product permanent magnets. In this work, we have examined the effects of soft magnetic α-Fe addition on the structure and magnetic properties of powders composed of hard magnetic Mn54.3Al44C1.7 compound. The optimum melt-spun ribbon precursor (with τ-phase structure, with magnetization of 88 emu/g and coercive field of 1.6 kOe) was obtained after annealing the ribbons at 500 ∘C for 20 min. After the combination between the soft and the optimized hard phase, the intensity of τ-phase peaks measured by X-ray diffraction decreases. These changes can also be seen in the magnetic properties. The coercivity (∼ 500 Oe) tends to decrease with the annealing temperature, while the magnetization tends to increase up to 141 emu/g. Evidence of good exchange coupling between particles of Mn54.3Al44C1.7 and α-Fe, in the produced composite, was proved by the hysteresis loop and its corresponding Thamm-Hesse analysis.
KeywordsMnAlC alloys Mössbauer spectroscopy Cryomilling
The authors would like to acknowledge professor Laura Lewis and her Nanomagnetism Group and professor Oliver Gutfleisch and his Functional Materials Group for their kind support during the doctoral visit of J.S. Trujillo Hernandez, Dr. Semih Ener for the SEM images, and M.Sc. Jeferson Piamba for the Mossbauer data.
This work was in part financed by Colciencias (contract No. 110671250407), Centro de Excelencia de Nuevos Materiales CENM-Univalle, and COLCIENCIAS, under Contract 110671250407. The authors specially acknowledge INAPEM (project EU 691235) for the kind support to our group.
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