Transformation‐Induced Magnetoelasticity in FeGa Alloys

Abstract

Global or local phase transformations are commonly used to create or improve useful properties of materials: the functionality of shape memory alloys is enabled by a global thermoelastic transformation. Transformation‐induced plasticity (TRIP) steels and the creation of transformation‐toughened ceramics are examples of materials innovations through local martensitic phase transformations. This research is undertaken to elucidate the nature of the large magnetostriction in FeGa alloys. An investigation of the evolution of the alloy's nanostructure in the varying magnetic fields of the objective lens of an electron microscope reveals the mechanism leading to the large magnetostriction; it is caused by a local martensitic transformation of the DO3 nanoprecipitates to a 6M phase, leading to transformation‐enhanced magnetoelasticity. The analysis of macroscopic elastic, magnetostriction, and magnetic torque data corroborates this finding.

Out of plane component of the magnetization of sputtered Fe72Ga28 layers

“…Theoretical calculations based on atomic density field theory have shown that, rather from direct nucleation, the formation of D03 occurs through a cascade of congruent orderings from A2, following the sequence A2 → B2 → D03 [33]. This is in accordance with the experimental evidence that the ordered phase B2 segregate from an A2 matrix [6]. Thus, when the samples are annealed, the formation of ordered phases (B2 and D03) is promoted [33,[17][18], the structural disorder is reduced as indicated by the increase of the crystallite size (Table I), and the squareness of the perpendicular hysteresis loops is decreased in the annealed state (Table I).…”

“…In the last years, there is a huge interest in the metallic FeGa system due to the discovery in 2000 of a large magnetostriction in these free rare-earth alloys [1][2]. Many of the published works have been devoted to the understanding of the origin of this enhanced magnetostriction in contrast with pure Fe [3][4][5][6][7][8][9][10][11][12]. It is remarkable that the largest deformation in Fe can be reached in the [100] direction with a (3/2)100 value of 22 ppm, whereas in FeGa alloys it can be obtained 430 ppm in that same direction [5].…”