The Study Of Perpendicular Magnetic Anisotropy In Heavy Metal/Co₂MnSi/Oxide Multilayer Films

In recent years,Magnetic Random Access Memory devices based on the current induced magnetization reversal have rapidly occupied a dominant position in the study of Magnetic Random Access Memory.One of the research focuses is how to effectively reduce the critical current density.The experiments show that the material with high spin polarization and the magnetic structure with perpendicular magnetic anisotropy（PMA）are beneficial to reduce the critical current density.Due to the characteristics of large spin polarization,small damping and high Curie temperature,Co-based Heusler alloys become an ideal ferromagnetic layer representative for realizing perpendicular magnetic anisotropy.Therefore,in this paper,Co₂MnSi（CMS）with typical high spin polarization is taken as the ferromagnetic layer,and a series of the Heavy Metal layer（Ta,Hf,Pd）/Co₂MnSi/Oxide layer（MgAl₂O₄,Al₂O₃）thin films are prepared on the glass substrate using the JGP-560 magnetron sputtering system.The specific experimental contents are as follows:（1）The effects of different Heavy Metal layers on the PMA of CMS/MgAl₂O₄（MAO）multilayer films were studied.The results showed that Ta/CMS（5 nm）/MAO（1 nm）and Hf/CMS（5 nm）/MAO（1 nm）multilayer films showed internal magnetic anisotropy（IMA）when Ta and Hf acted as Heavy Metal layers.However,Pd/CMS/MAO multilayer showed PMA,when Pd acted as Heavy Metal layer.3 nm thick Pd barrier layer was inserted at the Ta/CMS interface of the Ta（6 nm）/CMS（5 nm）/MAO（1 nm）multilayer,the film showed PMA.Combined with relevant experimental reports and our experimental result,we believe that Pd insertion layer can effectively block the capture of O by Ta and Hf layer due to its good stability and large electronegativity,so as to ensure an appropriate amount of orbital hybridization at the CMS/MAO interface.（2）In the experiment,a new tunnel barrier material MAO was selected as the oxide material.The effects of experimental parameters on PMA of Pd/CMS/MAO multilayer films,such as substrate temperature,MAO thickness,CMS thickness and oxygen input during oxide preparation,were systematically studied.Results show that a moderate amount（2 sccm）of oxygen injected into the MAO oxide layer when sputtering is beneficial to obtain PMA.Low or excessive oxygen flow will lead to the disappearance of PMA in thin films.In addition,it was found that PMA had a strong dependence on the thickness of CMS layer and MAO layer.When the CMS thickness was 5 nm,the PMA of Pd（6 nm）/CMS/MAO prepared under the substrate temperature of 350℃was the strongest,with a value of about 0.579×10⁶ erg/cm³.For t_MAO=1nm,PMA can be adjusted within a wider t_CMSMS range（4-5.7nm）.For t_CMS=5 nm,the structure can maintain PMA within a t_MAOAO of 0.9–1.3 nm.Finally,the analysis shows that the realization of PMA in Pd/CMS/MAO films is attributed to the dual interface effect of Pd/CMS and CMS/MAO.（3）Al₂O₃ was used as the Oxide layer in the experiment,the effect of Al₂O₃ thickness on the PMA of Pd（6 nm）/CMS（5 nm）/Al₂O₃(t_Al2O3)multilayer prepared at the substrate temperature of 350℃was explored.The results show that the multilayer films showing PMA are in a certain thickness of Al₂O₃ layer.When t_Al2O3=2.5 nm,PMA is the strongest and K_effff reaches its maximum value of 0.498×10⁶ erg/cm³.