Giant magnetoresistance and magnetic properties of CoFe/Cu multilayer films: Dependence of electrolyte pH

Abstract

The effect of NaOH with different concentrations on CoFe/Cu multilayer films was studied between pH=3.70 and pH=2.70. The effect of different electrolyte pH from 3.7 to 2.7, which was obtained at various NaOH concentrations, on CoFe/Cu multilayer films was studied. The structural studies by x-ray diffraction (XRD) revealed that the multilayers have face-centered cubic structure. The preferential orientation of the multilayer is in the (220), (111), (111), and (222) direction at pH=3.7,3.3,3.0 and 2.7, respectively. It was observed that at pH=3.0, the film composition, by energy dispersive x-ray spectroscopy (EDX), contains 3.22 at. Co % and 96.78 at. Cu %, and at low pH (2.7), 10.58 at. Co %, 4.18 at. Fe % and 85.24 at. Cu %. Magnetoresistance measurements made at room temperature showed that all films exhibited giant magnetoresistance (GMR), which was affected by the electrolyte pH. The observed GMR values are 4.0 %, 4.6 %, 4.2 %, and 12 % at the pH values of 3.7, 3.3, 3.0 and 2.7, respectively. Magnetic measurements of the films were made at +/- 20 kOe by using ADE EV 9 model a vibrating sample magnetometer. The magnetic measurements revealed that the coercivity of the films increased from 70 Oe to 93 Oe and stayed there, and the saturation magnetization monotonically increased form 7.40 emu/g to 17.05 emu/g with decreasing electrolyte pH from 3.7 to 2.7.