Magnetic properties and microstructure of lanthanum-doped Mn-Al and Mn-Al-C permanent magnets

Abstract

(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, T c, coercivity, iH c, and saturation magnetization, M s, were determined. Phase analysis revealed that Al8LaMn4 precipitates were produced due to the lanthanum addition. A slight increase in the iH c was observed for x ≤ 0.3 in the cast MnAlLa alloys. No significant changes in lattice parameters and T c were observed for these lanthanum-doped alloys. For sintered isotropic magnets, which were prepared by conventional powder metallurgy processes, the iH c 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 iH c may be due to the fine precipitates of lanthanum in the grain boundaries.