Giant enhancement of magnetostrictive response in directionally-solidified Fe₈₃Ga17Er_x compounds

We report, for the first time, correlations between crystal structure, microstructure and magnetofunctional response in directionally solidified [110]-textured Fe₈₃Ga₁₇Er_x (0 < x < 1.2) alloys. The morphology of the doped samples consists of columnar grains, mainly composed of a matrix phase and precipitates of a secondary phase deposited along the grain boundary region. An enhancement of more than ~275% from ~45 to 170 ppm is observed in the saturation magnetostriction value (λ_s) of Fe₈₃Ga₁₇Er_x alloys with the introduction of small amounts of Er. Moreover, it was noted that the low field derivative of magnetostriction with respect to an applied magnetic field (i.e., dλ_s/dH_app for H_app up to 1000 Oe) increases by ~230% with Er doping (dλ_s/d_{Happ, FeGa} = 0.045 ppm/Oe; dλ_s/dH_{app, FeGaEr} = 0.15 ppm/Oe). The enhanced magnetostrictive response of the Fe₈₃Ga₁₇Er_x alloys is ascribed to an amalgamation of microstructural and electronic factors, namely: (i) improved grain orientation and local strain effects due to deposition of Er in the intergranular region; and (ii) strong local magnetocrystalline anisotropy, due to the highly anisotropic localized nature of the 4f electronic charge distribution of the Er atom. Overall, this work provides guidelines for further improving galfenol-based materials systems for diverse applications in the power and energy sector.