Studies of electrical resistivity and magnetic properties of nanocrystalline CoFeCu thin films electrodeposited from citrate-added baths

摘要

In this study, nanocrystalline CoFeCu thin films were electrodeposited at different current densities from baths with natural pH (around 5.2) and containing 20 g/L citrate sodium. The relationship of films structure with soft magnetic properties and electrical resistivity, which are required for new generation magnetic head core, were investigated. SEM, EDS, XRD, TEM, VSM and four probe-point methods were used for characterization of the deposited films. The deposited films exhibited very uniform and homogenous structure with co-axis grains (confirmed by (111) and (110) poles figures and TEM images) throughout the coating. Overall, it was noticed that increasing current density from 1 to 24 mA/cm~2 reduced both grain size (from 63 to 8 nm) and coercivity (from 20 to 1 Oe) of the films. In addition, plotting Log (Hc) versus Log (D~6) demonstrated that the coercivity of the films followed "D~6 law". Moreover, increasing current density changed phase structures of the films from FCC (Cu)+FCC (Co) to FCC (Co) and then to FCC (Co)+BCC (Fe). The double phase films exhibited the lowest coercivity in comparison with single phase films due to their finer grain size. However, grain size had no effect on saturation magnetization of the films. An increase in current density up to 10 mA/cm~2 also caused the substitution of diamag-netic copper with cobalt and iron in the deposit which led to reduction in saturation magnetization. Increasing current density also led to increasing grain boundaries in the deposits and hence, according to "scattering hypotheses", enhanced the electrical resistivities.