HOTHERSALL MEMORIAL AWARD LECTURE 2009 Nano-electrodeposition for hard magnetic layers

Institute of Metal Finishing Electrocrystallisation must be carefully controlled in order to define a magnetic deposit at a nanolevel. A rational approach to the electrodeposition processes in order to control them is presented, taking into consideration and comparing the electrokinetic behaviour of the elements and the electrodeposit structure, resulting from the electron exchange reaction at the cathodic surface. Transient electrokinetic parameters were obtained with the secondary current pulse technique, where a square galvanostatic pulse of a few microseconds' duration is overimposed on the cathode while electrodeposition is running. Two parameters are measured - the transient Tafel slope and the adsorption pseudocapacitance; while a third parameter, the diffusive time constant, must be introduced if the overvoltage does not arrive at a steady state during the short pulse period. These parameters are related to the growth of different structures; this is important for most deposition processes, in particular for nano-electrodeposition of magnetic layers. Two processes for depositing hard magnetic layers are examined: cellular electrodeposition of Co giving hard layers with high magnetic moment, and electrodeposition of CoPt alloys, with high coercivity even at a relatively high thickness. The interactions between Co and Pt during the deposition process and in the deposited layer are underlined.