Magnetic properties and microstructure of lanthanum-doped Mn-Al and Mn-Al-C permanent magnets
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(Mn0.54Al0.46) 100−xLax and (Mn0.535Al0.448C0.017) 100−xLax alloys, with x up to 0.9, were synthesized and examined by powder X-ray diffraction and magnetic measurements. Lattice parameters, Curie temperature, Tc, coercivity, iHc, and saturation magnetization, Ms, were determined. Phase analysis revealed that Al8LaMn4 precipitates were produced due to the lanthanum addition. A slight increase in the iHc was observed for x ≤ 0.3 in the cast MnAlLa alloys. No significant changes in lattice parameters and Tc were observed for these lanthanum-doped alloys. For sintered isotropic magnets, which were prepared by conventional powder metallurgy processes, the iHc was enhanced on doping with lanthanum. The (BH)max values were also increased. The increment of (BH)max was about 16% for x = 0.3. Higher lanthanum intensity at grain boundaries was observed on examination of the energy-dispersive X-ray spectra (EDX). The reasons for the increase in iHc may be due to the fine precipitates of lanthanum in the grain boundaries.
KeywordsMicrostructure Magnetic Property Lanthanum Permanent Magnet Curie Temperature
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