ELECTROCHEMICAL SYNTHESIS OF MAGNETIC MATERIALS FOR MAGNETIC RECORDING AND MEMS APPLICATIONS
ABSTRACT With the increase in the areal density for magnetic recording disks, the bits are becoming smaller so that more bits can be accommodated in a given area of disk. However, there is a certain limit up to which the bits can be made smaller until it reaches the superparamagnetic limit, where bits become thermally unstable. In order for bits to be stable, high coercivity media is needed and the flux coming out from the writer head should be high enough to switch the high coercivity medium bits. Hence Cobalt Iron (Co37Fe63) alloys having the highest magnetic flux density of 2.4 T are used for this purpose. Sulfur containing additives like saccharin are incorporated in the CoFe electrodeposition bath to provide desirable properties like low stress, low coercivity and fine grain size to the deposit. The effect of saccharin incorporation during electrodeposition process on the properties of CoFe films is studied in this research. In-situ stress measurements were performed to determine the reduction in stress with increasing saccharin concentrations in the bath and an analytical model was developed to explain phenomenological dependence of the maximum stress level in CoFe films as a function of saccharin concentration in the bath. However, saccharin incorporation in CoFe bath lowers the corrosion resistance of CoFe films. The corrosion potential dependence on the sulfur incorporation mechanisms in CoFe films was studied via an analytical model based on the mixed potential theory. As bit size decreases, new magnetic sensors that provide high sensitivity and increased magnetoresistance ratio have to be developed. As a part of this research, the novel magnetic field sensors were fabricated based on electrodeposited CoFe nanocontacts and demonstrated magnetoresistance ratio as high as 3000%. The CoFe nanocontacts, ~70 nm in diameter, embedded in insulating Al2O3 layer which separates two plane parallel ferromagnetic layers represent the basic magnetic field sensor design. The magnetoresistance curves of these sensors displayed properties characteristic of both tunneling and ballistic transport of electrons by domain wall scattering. Hence, low temperature measurements were performed to understand the transport mechanisms of electrons in these electrodeposited magnetic nanocontacts.