Electrodeposition of cobalt-rich cobalt-platinum magnetic films: An electrochemical, structural, and magnetic study

In this dissertation, Co-rich Co-Pt alloys that possess perpendicular magnetic anisotropy were electrodeposited from an alkaline electrolyte. The deposition process was investigated by chemical and electrochemical methods. The microstructure and magnetic properties of the resulting films were thoroughly characterized.; We have found that the use of the Pt complex Pt(NH3) 2(NO2)2 and the addition of NaH2PO 2 favor the growth of Co-Pt along its hcp c-axis. The perpendicular orientation was found to be favored in the initial stage of growth by the epitaxial effects induced by a (00.1)-oriented Ru seed layer, and further stabilized by the electrochemical growth habit. Correspondingly, the films display perpendicular magnetic anisotropy. At small plating current, cobalt reduction is kinetically controlled; as current increases, the electrodeposition process becomes diffusion-controlled. Platinum reduction is diffusion controlled within the investigated current range. When plating current is above 10mA/cm 2, reduction of both metals is diffusion controlled, resulting in an almost constant film composition.; The utilization of NaH2PO2 not only yields perpendicular orientation, but also decreases the oxygen content in the deposits, especially at small current density. Thin films deposited at 10mA/cm2 contain very low oxygen (∼2%), and the magnetization process follows a domain nucleation-controlled mechanism. Films deposited at higher current densities contain higher oxygen. Especially, higher oxygen content was detected at grain boundaries, where most likely magnetic domain walls are pinned. Magnetization of these films thus follows a domain wall pinning controlled mechanism.; When current is above 10mA/cm2, film composition remains constant irrespective of plating current; however, the variation in growth rate induces partial formation of a metastable structure with short range chemical ordering. By means of EXAFS, the coordination number of Co-Pt bonds in the films deposited at 10-50mA/cm2 was found to be larger along the c-axis than in the in-plane direction. On the contrary, films deposited at 100mA/cm2, whose magnetic anisotropy constant is similar to that of bulk material, didn't show any chemical anisotropy. The anisotropy in chemical ordering is strongly correlated to the magnetic anisotropy being larger than that of bulk alloys; the short range seems thus responsible for the exceptionally high magnetic anisotropy observed.