Preparation And Characterization Of Co₂MnSi Thin Films

With the development of microelectronics technology,the size of the computer chip has reached submicron size,in order to increase the processing capacity and information storage,the corresponding device size is bound to the nano-level development.This requires that the material still need to maintain a high degree of coincidence of the spin orientation and that the structural properties are absolutely stable.In the moment,ordinary dilute magnetic semiconductors have been difficult to maintain their performance,but semi-metallic ferromagnets that compatible with the semiconductor is considered the ideal component of magnetic electronic devices in future.Co₂MnSi?CMS?has attracted much attention,because it has a large energy band gap of0.4 eV for minority-spin band and a high Curie temperature?985 K?.The half-metallic band structure in the CMS Heusler alloys is predicted to be sensitive to the site-disordered state,suggesting that a high degree of site order is necessary to realize half-metallic behavior in practice.Therefore,one requirement for successfully using CMS as a spin injection source is the defined growth of thin films with high crystal quality.On the other hand,Si is considered to be a superior semiconductor owing to its long spin lifetime and overwhelming dominance in the semiconductor industry.However,the desired half-metallic magnetic property is usually lost at the interface of half-metals and Si.So it is necessary to determine the structural and ferromagnetic properties of CMS on Si substrate.However,these properties are yet to be examined experimentally and very few relevant reports exist in the literature.At present,the preparation of CMS film method mainly includes MBE,high temperature melting method,magnetron sputtering method and so on.Among them,the magnetron sputtering method is the most common one preparation method,because of its easy operation,low cost,high repeatability.In this work,the CMS film was prepared by this method.And the effects of their properties on the structure of CMS films were investigated by controlling variable method,include buffer layer?Ta/Cr?,film thickness?25/50/75/100 nm?and annealing temperature?400/500/600/700 ^oC?.Research indicates:1.The addition of buffer layer affects the microstructure and magnetic properties of CMS films,when the buffer layer changes,the effect is also changing,and the soft magnetic properties of the films deposited with Ta are stronger than that of the films deposited with Cr.The optimum buffer layer thickness can make the CMS films structure and properties get better.2.With the increase of the film thickness,the CMS film has better B2 ordered phase,the magnetization of the film increases,and the coercivity increases first and then decreases,it is caused by the grain size effect.3.The increase of annealing temperature is beneficial to the growth of CMS film,but the high annealing temperature will aggravate the diffusion of buffer layer,which leads to the decrease of magnetization and increase of coercivity.The optimum process parameters of the preparation of CMS film were obtained,5 nm Ta was the buffer layer,the thickness of the sputtered film was 100 nm and annealed at 600°C for 1h in vacuum.The surface of the film was dense which has a B2 ordered phase,the film magnetization is 850.84 emu/cc,and the coercivity is 61.32 Oe.