Tetragonal magnetostriction and magnetoelastic coupling in Fe-Al, Fe-Ga, Fe-Ge, Fe-Si, Fe-Ga-Al, and Fe-Ga-Ge alloys

This paper presents a comparative study on the tetragonal magnetostriction constant, lambda(gamma,2), [-(3/2) lambda(100)] and magnetoelastic coupling, b(1), of binary Fe(100-x)Z(x) (0 < x < 35, Z - Al, Ga, Ge, and Si) and ternary Fe-Ga-Al and Fe-Ga-Ge alloys. The quantities are corrected for magnetostrains due to sample geometry (the magnetostrictive form effect). Recently published elastic constant data along with magnetization measurements at both room temperature and 77K make these corrections possible. The form effect correction lowers the magnetostriction by similar to 10 ppm for high-modulus alloys and by as much as 30 ppm for low-modulus alloys. The elastic constants are also used to determine the values of the magnetoelastic coupling constant, b(1). With the new magnetostriction data on the Fe-Al-Ga alloy, it is possible to show how the double peak magnetostriction feature of the binary Fe-Ga alloy flows into the single peak binary Fe-Al alloy. The corrected magnetostriction and magnetoelastic coupling data for the various alloys are also compared using the electron-per-atom ratio, e/a, as the common variable. The Hume-Rothery rules link the e/a ratio to the regions of phase stability, which appear to be intimately related to the magnetostriction versus the solute concentration curve in these alloys. Using e/a as the abscissa tends to align the peaks in the magnetostriction and magnetoelastic coupling for the Fe-Ga, Fe-Ge, Fe-Al, Fe-Ga-Al, and Fe-Ga-Ge alloys, but not for the Fe-Si alloys for which the larger atomic size difference may play a greater role in phase stabilization. Corrections for the form effect are also presented for the rhombohedral magnetostriction, lambda(epsilon,2), and the magnetoelastic coupling, b(2), of Fe100-xGax (0 < x < 35) alloys. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3674318]