Influence of ordering on the magnetostriction of Fe–27.5 at. % Ga alloys

Fe–Ga alloys with compositions near 27.5 at. % Ga (26–29 at. %) can be heat treated to obtain ordered phases based on α″ (ordered bcc), D019 (ordered hexagonal), and L12 (ordered fcc) structures. This work presents an evaluation of how the different ordering treatments influence the magnetostriction in cast polycrystalline Fe–27.5 at. % Ga alloy. Alloy samples were annealed first in the disordered bcc (A2) phase region to obtain a disordered bcc solid solution, followed by ordering-heat treatment in the appropriate temperature region of stability of each of the ordered phases. X-ray diffraction was used to characterize the phases present prior to and after heat treatments. Magnetostriction measurements were carried out at different prestress levels in the range of 0–50 MPa. Magnetic properties were measured using a vibrating sample magnetometer. Annealed Fe–27.5 at. % Ga sample with a disordered bcc (A2) structure and a weak [110] texture showed a magnetostriction value of 115×10−6. The α″ ordering treatment resulted in a small decrease of saturation magnetostriction. Magnetostriction decreased to negligible or small negative levels after D019 and L12 ordering treatments.