Preparation And Study Of Magnetic Ultrathin Films For Spin Electronic Device

Magnetic thin films that with perpendicular magnetic anisotropy(PMA)have important application in MRAM(Magnetic Random Access Memory),racetrack memory and spin logic devices,which have attracted extensive attention.In common spin electronic devices,Co FeB thin films and Co/Ni multilayers are the ideal thin film materials for it benefits of large perpendicular magnetic anisotropy and low damping constant.Currently,the latest technology requires that the film thickness in the spintronic devices is about the nanometer scale,which puts forward higher requirements on the preparation of magnetic thin films.This involves some basic problems in material science,therefore it is very important to study the preparation of magnetic ultrathin films from the perspective of material science and discuss the influence of the preparation conditions on their microstructure and magnetism.This paper mainly studied how to obtain the good perpendicular magnetic anisotropy of CoFeB films and Co/Ni multilayers film,and discussed the thickness dependence of perpendicular magnetic anisotropy in CoFe B films,the effect of type and the growth mode of the buffer layer,as well as the effect of film deposition sequence on the perpendicular magnetic anisotropy of CoFeB films.For Co/Ni multilayer films,we firstly studied the buffer layers' influence on the perpendicular magnetic anisotropy;then we investigated how the magnetic layers thickness and the repetition nubmer of Co/Ni multilayers influence the films' perpendicular magnetic anisotropy.We also discussed the physical mechanism of the magnetic layers thickness and the number of cycles of Co/Ni multilayers influence of the domain wall structure.Finally,the following conclusions are drawn:1.In the structure of Ta/CoFeB/MgO,When the thickness of magnetic layer CoFeB is between1.0 nm and 1.4 nm,the films show good perpendicular magnetic anisotropy.And when the thickenss of CoFe B is 1.2 nm,the film shows the best perpendicular magnetic anisotropy.A dead layer thickness is determined to be 0.3nm at Ta/CoFe B interface.2.The Co FeB films grown on Pt and W buffer layer do not show good perpendicular magnetic anisotropy because of the following factors.Firstly,there are different interface anisotropy atvarious heavy metal/magnetic layers' interface.Secondly,the thin W and Pt buffer layer tends to form an island structure at low sputtering rate,which is harmful for obtaining CoFeB film with good perpendicular magnetic anisotropy,However,by inserting a Ta layer under the Pt layer,which improve the Pt substrate's growth environment,we were able to obtain the Co FeB films with good perpendicular magnetic anisotropy.3.For the CoFeB-based film stack,changing the deposition order of oxide layer and heavy metal layer will greatly affect the perpendicular magnetic anisotropy of the films.This is because MgO layer will form rough interface during the film growth process,making CoFe B layer form granular films or more island-like structures,which deteriorates the perpendicular magnetic anisotropy of the films.4.The Pt and Ta/Pt seed layer is effective to induce(111)orientation in Co/Ni multilayer films,and therefore enhance the perpendicular magnetic anisotropy of the films.But the Ta buffer layer can not only provide a good growth environment for the(111)orientation growth of Co/Ni multilayers,and also reduce the roughness of the interface between the seed layer and the magnetic layer,significantly enhance the perpendicular magnetic anisotropy of the Co/Ni multilayers.5.Increasing the thickness of Co/Ni multilayer film and the repetition number can induce bow-tie shape hysteresis loops and reduce the domain width of the thin films.This is because the increase of the magnetic layer and the repetition number will increase the magnetostatic energy of the film.And small domain forms to reduce the magnetostatic energy,due to the competitive relationship between the domain wall energy and the magnetostatic energy.Therefore,the increase of magnetostatic energy is the main reason for the variation of the domain size in Co/Ni multilayers.