Strain-mediated magnetoelectric control of tunneling magnetoresistance in magnetic tunneling junction/ferroelectric hybrid structures

Because of the wide selectivity of ferromagnetic and ferroelectric (FE) components, electric-field (E-field) control of magnetism via strain mediation can be easily realized through composite multiferroic heterostructures. Here, an MgO-based magnetic tunnel junction (MTJ) is chosen rationally as the ferromagnetic constitution and a high-activity (001)-Pb(Mg$_{1/3}$Nb$_{2/3}$)$_{0.7}$Ti$_{0.3}$O$_{3}$ (PMN-0.3PT) single crystal is selected as the FE component to create a multiferroic MTJ/FE hybrid structure. The shape of tunneling magnetoresistance (TMR) versus in situ E-fields imprints the butterfly loop of the piezo-strain of the FE without magnetic-field bias. The E-field-controlled change in the TMR ratio is up to $-$0.27% without magnetic-field bias. Moreover, when a typical magnetic field ($\sim \pm 10$ Oe) is applied along the minor axis of the MTJ, the butterfly loop is changed significantly by the E-fields relative to that without magnetic-field bias. This suggests that the E-field-controlled junction resistance is spin-dependent and correlated with magnetization switching in the free layer of the MTJ. In addition, based on such a multiferroic heterostructure, a strain-gauge factor up to approximately 40 is achieved, which decreases further with a sign change from positive to negative with increasing magnetic fields. This multiferroic hybrid structure is a promising avenue to control TMR through E-fields in low-power-consumption spintronic and straintronic devices at room temperature.     

简单紧凑高刚性扫描隧道显微镜的研制

本文展示了一台自主研制的扫描隧道显微镜,它的主要特色是利用了一个内壁抛光的蓝宝石导向管作为扫描头的导轨,从而形成了较短的探针到样品的机械回路. 该导向管里面是一个被弹簧片夹持的方形滑杆,而压电扫描头安装在该滑杆上使得扫描隧道显微镜本身结构比较简单、紧凑、刚性. 同时蓝宝石良好的热导率又有利于提高显微镜的热稳定性. 为了证明该扫描隧道显微镜的性能,本文给出了高质量的石墨原子分辨率图像.     

利用扫描隧道显微镜在溶液中直接观测过渡族金属硫属化合物

本文利用自制的溶液扫描隧道显微镜在溶液环境下直接观测到TiSe₂、MoTe₂和TaS₂样品的原子分辨率图像. 通过将单晶样品在溶液中直接解理,可以保护解理过的新鲜样品表面在几个小时内不会被严重污染. 利用自行搭建的溶液扫描隧道显微镜,首先观察到了TiSe₂活泼样品的原子分辨率图像,并观察到了TiSe₂表面所特有的点缺陷和三角形缺陷结构. 此外,还观察到了MoTe₂的原子分辨率超结构和TaS₂表面的电荷密度波结构. 结果表明：在室温、溶液环境下能更高效的研究过渡族金属硫属化合物等活泼样品的表面电子态结构,同样适用于溶液环境下的电催化和电化学研究.