Fe80Ga20 films for magnetostrictive applications

Electrochemical deposition offers a simple and inexpensive method to produce functional coatings on large surfaces and in complex nanostructured geometries. Our research focusses on alloy coatings with special magnetic properties such as high magnetostriction, or the magnetic shape memory effect, which exhibit a high application potential for micro- and nano-dimensioned sensors and actuators.

Galfenol – an Fe-Ga alloy containing around 20 at.% Ga – combines high magnetostriction with good mechanical properties and is therefore promising to replace rare earth alloys such as Terfenol-D (Tb_0.3Dy_0.7Fe₂). However, its electrochemical deposition has been studied very little. Main challenges are the rather negative deposition potentials of the involved metals causing strong hydrogen evolution and low reproducibility and the strong tendency of gallium ions to hydrolyze and to form insoluble oxidic species, which are incorporated into the deposited films.

We have recently shown that dense and homogeneous Fe-Ga films (see fig., top) with the desired composition close to Fe₈₀Ga₂₀ can be successfully deposited from aqueous solutions of the simple metal salts at low pH values. By optimized pre-treatment and pulsed potential conditions the oxygen content in the films could be reduced to less than 1 at.%. The films show a (110) Fe₃Ga fibre texture and a saturation magnetization of up to 1.7 T (fig., bottom) which approaches the values for bulk single crystals of 1.75 T, confirming the high quality of the films.

[1] D. Iselt et al. Electrochim. Acta 56 (2011) 5178. URL