Nanoscience and Microsystems ETDs

Jamin Pillars

Publication Date

2-1-2016

Abstract

Magnetostrictive CoFe films were investigated for use as magnetoelastic tags or sensors. The ability to electrodeposit these films enables batch fabrication processes to pattern a variety of geometries while controlling the film stoichiometry and crystallography. In current research looking at CoFe, improved magnetostriction was achieved using a co-sputtering, annealing, and quenching method1. Other current research has reported electrodeposited CoFe films using a sulfate based chemistry resulting in film compositions that are Fe rich in the range of Co0.3-0.4Fe0.7-0.6 and have problems of co-deposition of undesirables that can have a negative impact on magnetic properties2, 3. The research presented here focused on maximizing magnetostriction at the optimal stoichiometry range of Co0.7-0.75Fe0.3-0.25, targeting the (fcc+bcc)/bcc phase boundary, and using a novel chemistry and plating parameters to deposit films without being limited to line of sight' deposition1. To obtain the desired compositional range, a chemistry was selected to allow for a higher ratio of Co while maintaining stability and limiting 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 (Bs) value as the Fe cation is oxidized2. This led to a deviation from the traditional sulfate based chemistry used to deposit CoFe alloy thin films and the inclusion of additives acting as oxygen scavengers to stabilize deposition. The characteristics of the deposited films were controlled through the additives, temperature, agitation, concentrations, current density, and duty cycle of the pulsing regime. After initial chemistry characterization to determine the kinetics and mass transfer limitations, samples were plated across a range of current densities and duty cycles onto copper tuning fork substrates that enabled magnetic testing to be performed. The samples were then analyzed with EDS to determine the composition. Magnetic testing was performed using super conducting quantum interference device measurements (SQUID), 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 stoichiometry and the plating parameters to characterize magnetostriction performance. Electrochemical studies were conducted to examine the kinetic rate for the reduction of the cobalt iron alloy as a function of additive concentrations. The oxygen scavenger additives were found to increase the kinetics while anodically shifting the reduction peak for the alloy. The leveling and brightening agents shifted the reduction peak cathodically and decreased the standard rate constant. Adjusting the concentration of ascorbic acid minimized the cathodic shift and decrease in the kinetic rate caused by the brightening additives.'

Keywords

Electrodeposition, Magnetostriction, Cobalt-Iron

Sponsors

This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000

Document Type

Dissertation

Language

English

Degree Name

Nanoscience and Microsystems

Level of Degree

Doctoral

Department Name

Nanoscience and Microsystems

First Committee Member (Chair)

Langlois, Eric

Second Committee Member

Petsev, Dimiter

Third Committee Member

Servov, Alexey

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