Magnetoelastic auxetic-like behavior in Galfenol: Experimental data and simulations.

Iron-gallium alloy (galfenol) is a body centered cubic (BCC) magnetostrictive alloy that, like many other BCC metals, is auxetic in the h110i{100} directions. For compositions of 12- 33 at.% gallium, Poisson ratio (n) values as low as 0.7 are observed along these directions in response to a uniaxial elastic force (tensile tests, resonant ultrasound spectroscopy, etc.). In 2014, Raghunath and Flatau first reported that galfenol also exhibits positive strain in both these directions when the uniaxial force applied along the h110i{100} directions is provided solely by a magnetic field, i.e., with no external mechanical/elastic force or stress being applied to the alloy [Raghunath and Flatau, IEEE Trans. Magn. 50(11), 1-4 (2014)]. The observed response is a result of the intrinsic, atomic-scale, bi-directionally coupled magnetoelastic properties of these alloys. In this paper, we advance the understanding of the intrinsic atomic-scale magnetoelastic coupling of the alloy that leads to the observed magnetoelastic auxetic-like behavior by presenting simulations developed based on density functional theory, which we show match the experimental findings and energy-based simulations. The elastic anisotropy and the electronic mechanisms that lead to magnetoelastic auxetic-like behavior in galfenol are discussed. [ABSTRACT FROM AUTHOR]