Study of microstructure and magnetic properties of electrodeposited nanocrystalline CoFeNiCu thin films

In this study the nanocrystalline CoFeNiCu thin films were electrodeposited from baths containing sodium citrate as a complexing agent and pH of around 5. Electrodeposition conditions were changed in order to achieve optimum soft magnetic properties which are required for new generation magnetic head core. SEM, EDS, XRD and VSM were used for characterization of the deposited films. The SEM micrographs of the deposited films exhibited no micro-voids and more uniform surface morphology compared with films electroplated from conventional baths (with low pH and no additives). According to X-ray diffraction patterns, the films electroplated at current densities lower than 4 mA/cm2 showed FCC (Cu) phase structure, and other films exhibited BCC (Fe) and/or FCC (Co) phases. Calculating grain size of the films by using Scherrer equation showed that all the coatings were nanocrystalline and double phase films had lower average grain size in comparison with single phase films. The VSM results demonstrated that the coercivity of the nanocrystalline films dramatically reduced with decreasing grain size and followed D6 law. However, grain size had no effect on the saturation magnetization, whereas the chemical composition significantly affected saturation magnetization of the films. The results also indicated that in order to obtain films with low coercivity and high saturation magnetization, the nickel and copper contents of the deposits must not exceed 12 and 5 at.%, respectively.

Research highlights
► Nanocrystalline CoFeNiCu soft magnetic thin films were electrodeposited.
► Using citrate ions and pH of about 5 affected films compositions and structure.
► The phase structures of the films consisted of FCC (Cu), BCC (Fe) and/or FCC (Co).
► The double phase films had the finer grain size (about 20 nm) than the single phase.
► The film composition affected the films saturation magnetization and its coercivity.