le R

ele e 2 anc lvan eas on 23# ved as shown in the cross section, Fig. 1b. Although a saturated calomel oc 0 © Downated between two values. At the less negative potential/lower cur-rent density, only Cu, the most noble metal present, is deposited, while at the more negative potential/higher current density, a ferro-magnetic alloy is deposited. To ensure that this alloy does not con-tain too high a proportion of nonmagnetic Cu, an electrolyte with very low Cu concentration is used, so that Cu deposition is mass-transfer limited when the less noble magnetic metals deposit.9 De-spite the consequent importance of Cu mass transport, very few investigations of GMR in electrodeposited multilayers were carried out under conditions where the transport was well controlled. Most studies used an unstirred electrolyte and natural convection, even though deposition in a cell with forced convection may be controlled more precisely and reproducibly. Nevertheless, in some cases, very high GMR values were obtained.2 Here we use a flow cell with well-defined hydrodynamic proper-ties to demonstrate the influence of Cu mass transport on the GMR of electrodeposited Co-Ni-Cu/Cu multilayers. A flow cell was used in preference to a rotating disk electrode because the stationary working electrode in a flow cell is very convenient to replace, which reference electrode could be mounted in the electrolyte reservoir, this could not be used at zero flow rate. In the first stages of this study, Cu plates were used as substrates, but the multilayers electrodeposited on them generally appeared very rough. Shiny multilayers were obtained when films of 25 nm Au/3 nm Cr sputtered on glass were used as substrates instead. The circular area on which deposition took place was defined by mask-ing the substrates with kapton tape, and a fine Au wire was placed in a ring around this area in contact with the substrate beneath the tape to minimize the influence of the substrate resistance. The electrolyte was similar to that used in previous studies of GMR in Co-Ni-Cu/Cu multilayers1,7,8 and was prepared by dissolv-ing fixed quantities of the appropriate salts in a fixed volume of pure deionized water. The electrolyte contained ~in moles per liter H2O