Magnetostrictive Co-Fe-Mn films were investigated for their use in fabricating magnetoelastic resonators. Electrodepositing these films enables batch fabrication of resonators with varying geometries and therefore, resonant frequencies, while controlling the film stoichiometry and crystallography. Boron, phosphorous, and molybdenum were used to increase the electrical resistivity and control film texture. Additionally, ascorbic acid and TMAB were used as “oxygen scavengers” to control the chemistry’s stability and limit the oxidation of the Fe²⁺ to Fe³⁺. As suggested by Osaka et al, Fe(OH)₃ is formed and included into the film resulting in a decrease of the saturation magnetic flux density (B_s) value as the Fe cation is oxidized[1,2]. Additives, such as Saccharin and Sorbitol, were added as grain refiners and stress reducers, enabling flat cantilever structures that did not bend out of plain due to intrinsic stress gradients.

The composition and phase of the deposited films were controlled by temperature, agitation, concentrations in the electrodeposition chemistry, current density, and duty cycle of the pulsing regime. The samples were analyzed with EDS to determine the composition and XRD to look at film texture. Magnetic testing was performed using super conducting quantum interference device (SQUID) magnetometry, as well as visual inspection of the displacement on a deposit stress analyzer as a magnetic field was applied to the films. The magnetostriction was then correlated to EDS and XRD results to identify phase, stoichiometry and the plating parameters to produce improved magnetostriction while maintaining low intrinsic stress. Annealing studies of these films were performed using a tube furnace with inert gas to heat past the Curie temperature and then cool in the presence of an applied magnetic field. The applied magnetic field direction and its correlation with magnetic properties and phase will be discussed.

Acknowledgement

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

References

1. Osaka, T., et al., A high moment CoFe soft magnetic thin film prepared by electrodeposition. Electrochemical and Solid State Letters, 2003. 6(4): p. C53-C55.
2. Elhalawaty, S., et al., Oxygen Incorporation into Electrodeposited CoFe Films: Consequences for Structure and Magnetic Properties. Journal of the Electrochemical Society, 2011. 158(11): p. D641-D646.