Soft Magnetic Properties and Electrochemical Behavior of Nanocrystalline CoFeCu Thin Films Electrodeposited from Citrate-Added Baths

Abstract

CoFeCu thin films were electrodeposited from baths with natural pH (instead of pH∼2.8 used in conventional baths) and containing different sodium citrate dosages. ChemEQL V.3.0 software was employed to study speciation diagrams of citrate-added CoFeCu bath with natural pH. At low sodium citrate dosage, Co++, Fe++, and Cu++ species were dominant in CoFeCu bath with natural pH (around 5.2). However, as dosage of sodium citrate in the bath increased, the concentration of complexed species (especially Co(C6H5O7)−, Fe(C6H5O7)−, and Cu(OHC6H5O7)2−) significantly raised. Cyclic voltammetry (CV) studies showed that the formation of complexed species in the bath shifted reduction potential of metals towards more negative potentials. Moreover, in order to deposit cobalt and iron simultaneously with copper, it was necessary to increase the reverse potential (E λ ) value gradually with sodium citrate dosage, otherwise, only copper would have deposited from citrate-added CoFeCu bath. Scanning electron micrographs illustrated that using natural pH (about 5.2) remarkably decreased the number of microvoids in the deposited films compared with the film deposited from conventional baths with pH level of 2.8. EDS, XRD, and VSM were also used for characterization of the deposited films. All deposited films exhibited nanocrystalline structures, and increasing sodium citrate into the baths led to reduction in grain sizes (D) and coercivity (H c) of the CoFeCu thin films. Plotting log(H c) versus log(D 6) demonstrated that films coercivity followed the “D 6 law”. There were only two phase structures (FCC (Co) or BCC (Fe)) observed in the X-ray diffraction patterns of the films. In addition, films with double-phase structures (FCC+BCC) showed finer grain sizes and therefore exhibited lower coercivity in comparison with single-phase (FCC or BCC) films. CoFeCu thin films deposited at higher dosages of sodium citrate (>20 g/L) were poor in diamagnetic copper and consequently showed higher saturation magnetizations.