Perpendicular magnetic tunnel junctions (MTJ) with a bottom pinned referencelayer and a composite free layer (FL) are investigated. Different thicknessesof the FL were tested to obtain an optimal balance between tunnelingmagnetoresistance (TMR) ratio and perpendicular magnetic anisotropy. Afterannealing at 400 $^\circ$C, the TMR ratio for 1.5 nm thick CoFeB sublayerreached 180 % at room temperature and 280 % at 20 K with an MgO tunnel barrierthickness corresponding to the resistance area product RA = 10Ohm$\mathrm{\mu}$m$^2$. The voltage vs. magnetic field stability diagramsmeasured in pillar-shaped MTJs with 130 nm diameter indicate the competitionbetween spin transfer torque (STT), voltage controlled magnetic anisotropy(VCMA) and temperature effects in the switching process. An extended stabilityphase diagram model that takes into account all three parameters and theeffective damping measured independently using broadband ferromagneticresonance technique enabled the determination of both STT and VCMA coefficientsthat are responsible for the FL magnetization switching.
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机译：研究了具有底部固定参考层和复合自由层（FL）的垂直磁隧道结（MTJ）。测试了不同厚度的FL，以获得隧穿磁阻（TMR）比和垂直磁各向异性之间的最佳平衡。在400℃下退火后，1.5nm厚的CoFeB子层的TMR比在室温下达到180％，在20K下达到280％，其MgO隧道势垒厚度对应于电阻面积乘积RA = 10Ohm $ \ mathrm {\ mu } $ m $ ^ 2 $。在直径为130 nm的柱形MTJ中测得的电压与磁场稳定性图显示了自旋传递转矩（STT），压控磁各向异性（VCMA）和温度在开关过程中的竞争。一个扩展的稳定相图模型，该模型考虑了所有三个参数以及使用宽带铁磁共振技术独立测量的有效阻尼，从而能够确定负责FL磁化切换的STT和VCMA系数。
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