Study On Copper-Cobalt Series Granular Films Prepared By Electrodeosited And Its Giant Magnetoresistance

Since the discovery of giant magnetoresistance(GMR) in 1988, the development and application of GMR material have attracted more attention from the scientists, and achieved great progress in the fields of physics and material science. Giant magnetoresistance can be considered as a part of nanoelectronics, and established new field of magnetoelectronics. The copper-cobalt series granular films were prepared by conventional method-electrodeposition in the paper, main influencing factors of giant magnetoresistance in granular films were studied and analyzed.First, influencing factors of electrodeposited process were analyzed. The components and particle size of the Cu-Co film were related with the concentration of the main salts and concentration of complexing reagent, pH value and current density. The films grown stage by stage during electrodeposited, the copper deposited on the surface of the cathode prior to cobalt, the cobalt deposited on the thin copper coating. The film was metastable state.Main influencing factors of giant magnetoresistance for CuCo granular film were analyzed. The results show that the MR of the films was changed by the content of Co content in the film, it was favorite to the GMR value that the content of magnetic component increase properly, the maximum of GMR was occurred when the content of cobalt is 20% in the films, the GMR would decrease if the ferromagnetic component was too much. Surface scanning for elements analysis and XRD show that the separation of Co grain was occurred during annealing, and part Co-rich regions was appeared.The annealing in vacuum can improve the GMR of the film. The maximum value of GMR was 3.85% which occurred at Cu80Co20 film after annealing at 450℃for 1h. With the annealing temperature increase, the electrical resistivity was dropped. The saturated magnetization Ms、coercive force Hc、remanence magnetization Mr were increased with improved annealing temperature by magnetic measurement.The phenomenological theory was used to fit the GMR value and magnetic data for Cu80Co20 film. The content of ferromagnetic phase was analyzed by the application of ferromagnetic theory, which indicated that the magnetic grain began to grow up and the size of supperparamagnetism particle increased in the films during annealing. The results were analyzed by phenomenological theory and effectiveness medium theory showed that the component and the size of magnetic grain in the film were important to GMR.In order to improve the phase separation for the film, the CuCoNi films were electrodeposited from the CuCo plating solutions added Ni2+. There was a linear relationship between Ni content in the films and Ni ion concentration in the baths. XRD results showed that the suitable content of Ni was favorable to the separation of magnetic particle in the films. More Ni addition would decrease the content of magnetic particles.The magnetic measurement indicated that GMR of as-deposited CuCoNi films was higher than that of the films without Ni addition, but after annealing, GMR of CuCoNi films was no more increase than the CuCo films. The saturated magnetization was bigger and coercive force was smaller than that of the films without Ni addition. The superparamagnetic particles changed to ferromagnetic particles during annealing process, and coercive force was promoted. The maximum value of GMR was 2.4% for 2.7% of Ni content in the films annealed at 450℃. The optimum structure of films was appeared. GMR decreased after annealing at temperature over 450℃.In order to gain the fine grain in the film, CuCo granular film was prepared by electrodeposition in the stable magnetic field. The composition of the film was changed with the intensity of the magnetic fields. When the magnetic fields was 0.6-0.8T at B⊥J, the Co content in the films was higher, and the Co deposition was restrained by stronger magnetic fields. The Co content was higher than 20% at B//J generally, and attach to 30% in 0.7T, which was due to effect of the Lorentz force and paramagnetic, and the influence of MHD.The magnetic field could promote the refined crystal grains of the plating at B⊥J. and the crystal grains of films were more bigger at B//J, which included more Co in the films, the condition that the agitation of the solution was strengthened at this case also effect the deposition. XRD result showed that Magnetic field effected the crystallization of the granular film at some extent, and preferred the orientation of (111) crystal plane.The films which deposited in magnetic fields at B⊥J promoted the value of GMR. The maximum of GMR in CuCo granular films which deposited in 0.6T magnetic field was 4.81% after 500℃annealed, which increased 25% than the films prepared without magnetic field, and the optimal annealing temperature enhanced to 500℃. The hysteresis loops indicated that granular film which prepared in 0.6T magnetic field at B⊥J after 500℃annealing 1h showed more well magnetic property than the films annealed at other temperature. The proportion of magnetic and superparamagnetic component in the films was optimal state, which promoted the scatting at interface and showed higher GMR.