X-ray diffraction analysis by Rietveld refinement of FeAl alloys doped with terbium and its correlation with magnetostriction

Abstract

Fe81Al19 polycrystalline alloys doped with Tb (0–0.25 at%) were obtained by arc melting. The introduction of Tb favors the formation of columnar grains in the microstructure of the alloys, which develops a texture in the [100] crystal direction. Microstructural examination shows that the alloys are composed in great proportion by the disordered body-centered cubic (bcc), A2 phase and by a small proportion of the ordered bcc, B2 phase. As a consequence of doping with Tb, the lattice parameter increases, so the calculated apparent crystallite size increases, indicating a decrease in dislocation density and therefore in microstrains. The change in the magnetostriction with the magnetic field, dλT/dH, is directly related to strain anisotropy that can favor the iron easy magnetization axis on the [100] direction. An increase in total magnetostriction is found in the doped alloys with a maximum of 90 × 10−6 at 300 K for the alloy containing 0.027 at% Tb. This enhancement is a threefold value of the undoped alloy, which is attributed to the smaller maximum strain value and the preferential orientation formation by the columnar grains.