Tuning the crystal structure and magnetic properties of CoNiFeB thin films

CoNiFeB thin films with a high saturation magnetic flux density (B _s) and a low coercivity (H_c) are used as core materials in high-density recording heads. Electroless deposition has proven to be an excellent process for the fabrication of metallic thin film structures, because it does not suffer from limitations associated with current density distribution and can therefore be used to create uniform coatings on substrates with fine and/or complex geometries. The crystal structure of CoNiFeB films, which is dependent on their chemical composition, can be controlled by changing the bath composition; however, to our knowledge, there is no report on tuning the chemical composition, crystal structure, and magnetic properties of CoNiFeB thin films only by the optimization of the electroless deposition parameters while maintaining the same concentration of salts in the bath. In this study, through the use of complementary techniques including AFM, SEM, XRD, EDS, and VSM, we show how the crystal structure of the CoNiFeB films can be tuned from a single-body-centered cubic (BCC) phase to a single face-centered cubic (FCC) phase with intermediate mixtures of BCC/FCC phases by only changing the pH and temperature of the electroless bath.