Study On Properties And Electrochemistry Mechanism Of CoNi Based Alloy Films Prepared By Magnetic Plating Technology

With the development of microelectromechanical systems,smaller size magnets are required as components.Permanent magnet films play a big role in the microelectromechanical system,which could be widely used in micro-driver,micro-sensor,energy collector and so on.Cobalt possesses high melting point,high hardness and better mechanical properties.It is found out that cobalt alloys have the advantage of compact structure and excellent corrosion resistance.It is more important that cobalt alloy films have optimal magnetic performance,not only can be used as a high density perpendicular magnetic recording medium,but also could instead of tiny magnets in the microelectromechanical system.Magnetic plating is considered as a new kind of technology in the process of thin films preparation,which could effectively improve deposition rate,refine coating grains,reduce surface roughness,improve magnetic properties and so on.This paper investigated the effects of magnetic intensities on electrochemical kinetics,surface morphology,structures,magnetic performance of cobalt based films during electrodeposition process.The conclusions are as following:(1)The study found out that cobalt electrochemical deposition belongs to a kind of irreversible diffusion controlled with three dimensional nucleation process.When the magnetic field is perpendicular to the electric field,it has a great effect on electrochemical process.MHD effect produced by perpendicular magnetic may reduce thickness of diffusion layer to improve ions transfer speed and deposition rate.When the magnetic field is parallel to the electric field,the electrochemical system is mainly affected by the magnetic field gradient force to hinder the deposition process of cobalt.With the introduction of parallel magnetic field,cobalt is magnetized and growing in the direction of magnetic field to form typical "mountain" structure films.(2)Nickel electrodeposition is considered as a kind of electrochemical control process.With the increase of the cathodic polarization,polarization current increases.Applying perpendicular magnetic field during nickel deposition helps to improve deposition current,accelerate nickel ions transfer rate and increase mass of deposition due to the thickness reducing of confusion layer.Dendrite shape structures could be observed in the perpendicular magnetic model.When the magnetic field is parallel to the electric field,nickel ions would be affected by magnetic field gradient force to accelerate migration rate and promote the electrochemical deposition process of nickel.(3)Electrodeposition of CoNi belongs to the typical anomalous codeposition process.With the increase of pH value near cathode,cobalt hydroxide colloid forming may restrain the nickel deposition to increase cobalt contents in the films.Higher cobalt concentration in the solution,more obvious anomalous codeposition could be observed.Perpendicular magnetic field would improve CoNi deposition current and decrease cobalt contents in the film.CoNi films with higher cobalt contents possess co-fcc and co-hcp structures with "rice" morphology.With the effect of parallel magnetic field,the intensity of CoNi(111)and Co(002)diffraction peaks gradually increase,proving that(111)and(002)are respectively two easy magnetization direction of CoNi and Co.(4)Introducing perpendicular magnetic field during CoNiMnP deposition process would help to improve polarization current and increase quality of films.After applying 1 T perpendicular magnetic intensity,the polarization current increases by 12.2% and deposition mass increases by 10.25%.Under the influence of perpendicular magnetic field,cobalt contents decrease.CoNi diffraction peaks appeared in 44.5°,51.8°,76.4 ° and 93.1° respectively with good crystalline structure.CoNiMnP alloy films possess very good vertical anisotropy.The introduction of the magnetic field is beneficial to increase the coercivity and saturation magnetization.The study found that CoNiMnP films prepared with 1 T magnetic field and 0.8 V deposition potential have better coercivity and remanence.