Extraordinary magnetoelasticity and lattice softening in bcc Fe-Ga alloys

Extraordinary magnetostrictive behavior has been observed in Fe-Ga alloys with concentrations of Ga between 4% and 27%. lambda(100) exhibits two peaks as a function of Ga content. At room temperature, lambda(100) reaches a maximum of 265 ppm near 19% Ga and 235 ppm near 27% Ga. For compositions between 19% and 27%, lambda(100) drops sharply to a minimum near 24% Ga and exhibits an anomalous temperature dependence, decreasing by as much as a factor of 2 at low temperatures. This unusual magnetostrictive behavior is interpreted on the basis of a single maximum in the magnetoelastic coupling \b(1)\ of Fe with increasing amounts of nonmagnetic Ga, combined with a strongly temperature dependent elastic shear modulus (c(11)-c(12)) which approaches zero near 27% Ga. lambda(111) is significantly smaller in magnitude than lambda(100) over this composition range, and has an abrupt change in sign from negative for low Ga concentrations to positive for a concentration of Ga near 21%. (C) 2003 American Institute of Physics.