Effect Of High Magnetic Field Annealing On Diffusion And Magnetic Properties Of Co/Cu Films

With the development of miniaturization and high frequency development of modern electronic devices,more and more attention has been paid to the research of thin film materials.When preparing and using thin-film devices,heat will transfer to the devices,and result in inter-film diffusion,especially in the polycrystalline film.Because grain boundary of the polycrystalline film can act as the rapid diffusion channel,the diffusion can occur at a lower temperature.Diffusion between thin films will cause a series of effects on the performance of thin film devices,such as Schottky barrier instability and the formation of metal silicide.In addition,an adhesive layer between a metal thin film and a substrate can be prepared by film diffusion,so that a film having poor adhesiveness is better bonded to a substrate.Therefore,it is necessary to study the diffusion behavior between films.Besides,in order to improve the sensitivity of the devices,it's necessary to control the magnetic properties of the films.High magnetic field has effects of Lorentz force,magnetization force and magnetic free energy.The application of high magnetic field annealing can affect the interdiffusion and magnetic properties of thin films.Therefore,high magnetic field annealing is introduced to study the interlayer diffusion behavior and magnetic properties of the multilayer films.Co/Cu multilayers are widely used in hard disk heads because of their giant magnetoresistance effect,and these hard disk heads have high read speed and high storage density.In addition,Co and Cu have low lattice mismatch,and Co will change its phase structure,so the diffusion behavior between Co and Cu is rather special.Because the diffusion of Co and Cu in Si substrate affects the diffusion between Co and Cu,different elements are preferentially deposited on the Si substrate,and different diffusion interfaces have different diffusion behaviors.Si(substrate)/Cu/Co bilayer film diffusion couple,Si(substrate)/Co/Cu bilayer film diffusion couple and Si(substrate)/Co/Cu/Co trilayer film diffusion couple were fabricated by vacuum deposition method.The films were annealed at 300?,400?and 500? under 0T and 11.5T magnetic field,respectively.The composition of the films was analyzed by XRD,the morphology and surface roughness of the films were analyzed by atomic force microscopy(AFM).The distribution of the films was analyzed by TEM scanning and XPS depth analysis.Finally,the magnetic properties of films were analyzed by vibrating sample magnetometer.The results show that:(1)Diffusion of Cu into the Si substrate is promoted by the application of a high magnetic field in the Si(substrate)/Cu/Co bilayer diffusion system,thereby decreasing the amount of Cu diffusing into the Co layer.Therefore,the Co content is higher than the case without the application of magnetic field,making more magnetic phase contained in the film samples.The saturation magnetization of the samples is higher than that without magnetic field at different annealing temperatures.When the samples are annealed at 300? and 400? with the application of magnetic field,the coercivity is increased due to the increase of surface roughness.When the samples are annealed at 500? with the application of magnetic field,the samples contain fcc Co and hcp Co,the coercivity of two mixed Co phases is bigger than single Co phase.(2)In the Si(substrate)/Co/Cu bilayer diffusion system,the application of high magnetic field at the annealing temperatures of 300? and 500? promotes the diffusion of Co atoms into the silicon substrate and Cu layer,which decreases the content of magnetic phase and then reduces the saturation magnetization of the samples.When the samples are annealed at 400?,there are similar distribution curves with and without the magnetic field,and the thickness and content of Co-rich layer change little,so the saturation magnetization of the sample is almost the same.Besides,the strong magnetic field promotes the diffusion of Cu atoms in the Co layer and increases the coercivity.(3)In the Si(substrate)/Co/Cu/Co trilayer diffusion system,when the samples are annealed at 300? and 500?,the distribution curves of the samples change little,so the saturation magnetization and coercivity change little.When the annealing temperature is 400?,the application of high magnetic field increases the width of the diffusion zone,increases the diffusion between Co and Cu,reduces the magnetic phase content of the samples,thereby reducing the.saturation magnetization of the samples.High magnetic field annealing at 400? reduces the surface roughness of the samples and therefore reduces the coercivity.