The effect of pH changes on the giant magnetoresistance of electrodeposited superlattices

We have studied the effect of electrolyte pH on the ''giant magnetoresistance'' in Co-Ni-Cu/Cu superlattices prepared by electrodeposition. Films grown at low pH (1.8 +/- 0.1) exhibited giant magnetoresistance (GMR) of over 15% while, depending on layer thicknesses, films grown at high pH (3.3 +/- 0.1) exhibited either predominantly anisotropic magnetoresistance (AMR) or much smaller GMR than possible at low pH. Also, the films grown at low pH were found to have a higher magnetization than those grown at high pH. The different magnetic and magnetotransport properties observed for different values of the electrolyte pH are accompanied by changes in the shapes of the current transients recorded during film growth and by changes in the composition of the superlattices. A possible explanation of these results is that reducing the electrolyte pH leads to a more abrupt interface between the ferromagnetic and nonmagnetic layers by suppressing Co dissolution.