物理科学与技术学院知识库

磁性隧道结在近二十年来一直都是凝聚态物理、信息工业和材料科学领域最火热的研究焦点之一，然而由于目前对纳米尺度下的磁性隧道结实际发生的磁化动力学关键过程缺乏直观、准确的了解，使其在进一步微型化的工业应用过程中碰到了瓶颈。本论文拟通过高真空溅射结合聚焦离子束电镜刻蚀技术制备不同尺度、结构的Ni75Fe25薄膜单元，借助洛伦兹（球差）透射电镜/电子全息技术和超高速图像采集系统，通过利用实验自主研发的纳米操纵器扫描电镜原位磁输运测量仪器原位施加磁场、实时观测Ni75Fe25薄膜阵列单元的磁化翻转的动态变化过程，系统研究边缘缺陷对磁性隧道结磁化翻转机制和自旋输运机制的影响，在纳米甚至原子尺度上掌握磁性隧道结磁畴结构、磁力线分布变化规律，为解决磁性隧道结微型化中各单元同一性差、写入临界电流密度过高等主要难题提供技术支持和理论依据。本论文的研究成果概括如下：
(1) 在实验室自主研发的基础上了改良了一种扫描电镜纳米操纵器原位磁输运测量仪，并对其技术性能进行了全面测试，纳米操纵器的移动范围可以达到14 mm, 三维运动精度达到2 nm；磁化样品台的磁场和样品间夹角能以0.003°的精度在 360 度平面内任意旋转；磁化样品台可以在样品附近施加高达 1800 Oe的磁场，并利用此设备测量Ni75Fe25薄膜的磁阻特性。
(2)  通过高真空溅射结合聚焦离子束电镜刻蚀技术制备不同尺度、结构的Ni75Fe25薄膜zigzag 模型、多边形单元阵列模型，借助洛伦兹（球差）透射电镜通过原位加磁场、实时观测Ni75Fe25薄膜纳米单元的原位加磁场诱导下磁化翻转的动态变化过程，并用微磁学模拟的手段，对畴壁翻转过程进行模拟，通过研究边缘缺陷的影响，在纳米尺度上掌握磁隧道结的磁畴结构，磁力线分布变化规律，并且可以设置不同形状的钉扎来调控畴壁的形状及运动过程。有助于解决磁隧道结单元在纳米尺度下边界条件对单元器件的钉扎影响。

The domain wall movement of size and shape-controlled Ni75Fe25 film Zigzag geometry will become a part of free layers of magnetic tunneling junctions (MTJs). They were prepared by means of a jointed methods involved to high-vacuum sputtering and focused ion beam etching techniques, which lead to achieve a high-quality and fully controllable preparation of various architectures of nanoscale MTJs. Their intrinsic and technical magnetic properties will be tested, which includes a deep investigation of the relationships of their atomic magnetic moments vs. temperature and atomic magnetic moments vs. external field. The physical mechanisms and principles how the dynamical magnetization, magnetic, and magneto-transparent behaviors of Ni75Fe25 film are influenced by their sizes, shapes, edge defects , and the proximity effects of electricity and magnetic field leakages will be studied at the nanoscale and atomic scale by using an advanced Cs-corrected transmission electron microscopy platform equipped with Lorentz lens, electron holography, which directly provide a simultaneous and dynamic view of the magnetization reversal processes, domain wall structures and magnetic fluxes of nano-MTJs. This project is believed to helpfully resolve the obstacles of the cell to cell variability and too high writing current critical density, which is significant to strengthen their technology maturity. The research results of this paper summarized as follows:
(1) Based on the laboratory's own research and development, a scanning electron microscope nanomanipulator in-situ magnetic transport measuring instrument was improved and its technical performance was fully tested. The nanomanipulator's moving range can reach 14 mm, and the three-dimensional movement accuracy reaches 2 nm; the magnetization sample stage magnetic field and sample angle can be rotated within a 360 degree plane with an accuracy of 0.003°; the magnetization sample stage can apply a magnetic field of up to 1800 Oe near the sample, and use this device to measure the magnetic resistance of the Ni75Fe25 film characteristic.
(2) By high vacuum sputtering with focused ion beam electron microscopy (FIB-SEM) etching technology preparation of different scales, the structure of zigzag Ni75Fe25 film model, polygon cell array model, with the aid of Lorentz-TEM、electronic holography and high-speed image acquisition system, by in-situ loading magnetic field, real-time observation Ni75Fe25 film nano cell in situ with magnetic field induced by the dynamic changes of the magnetization reversal process, by means of micro magnetic simulation, simulated the process of domain wall flip, through study the influence of the edge defects, to master the magnetic tunnel junction in the nanoscale magnetic domain structure, distribution of magnetic line of force, and can set different shape nail pierced to control the shape of a domain wall and the movement process. Help to solve the magnetic tunnel junction unit in the nanoscale pinning effect of boundary conditions on the unit device.