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College Park, Maryland      June 6 - 10 , 2004

M3-A2 (2:00 PM): Compositional variation of the phonon dispersion curves of bcc Fe-Ga alloys

J.L. Zarestky, O. Garlea (Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011), T.A. Lograsso (Ames Laboratory, Metal and Ceramic Sciences, Iowa State University, Ames , IA 50011), C. Stassis (Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011)

The Fe-Ga system is of considerable scientific and technological importance(1) because it is a unique example of a ductile polycrystalline magnetostrictive alloy. Motivated by elastic constant measurements(1) which indicate that the shear elastic constant 1/2(C11-C12) decreases with increasing Gallium concentration and extrapolates to zero at approximately 26 at. % Ga, we began a systematic study of the phonon dispersion curves of these alloys as a function of concentration. The TA2[110] transverse phonons, with polarization in the [1-10] direction, show considerable softening as the composition is varied from 10.8 to 22.5 at. % Ga. This softening occurs not only at low wave vectors (q's) (elastic wave region) but at q's extending to the zone boundary and is greater than expected from the difference in Fe and Ga masses. It is correlated with the large increase in magnetostriction observed in this range of compositions. The softening of the dispersion curves in other symmetry directions will also be discussed.

(1) M. Wuttig et al. - Applied Physics Letters, Vol. 80, No. 7, 1135, 2002

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