Misfit Strain, Dislocations and Magnetism in Epitaxial Nano-Dots

0105423O‘Handley用新的、功能强大的ME系数测量技术研究了外延磁性纳米点中应变和位错的影响。利用干涉光刻技术制作了横向特征尺寸为25 nm、厚度为2~20 nm的高度规则的磁点和椭圆形图形阵列，研究了有限的横向尺寸对应变消除和ME效应的影响。该项目的重点是在铜缓冲的Si(001)上外延Ni80Fe20和钴薄膜，这是许多磁性薄膜应用的重要材料。薄膜和点阵列的表征利用(A)BNL的同步加速器x射线衍射仪来确定应变，(B)扭矩磁测法来表征磁各向异性，(C)振动样品磁测法来确定饱和磁化强度和居里温度，(D)一阶和二阶ME耦合系数的微分电容测量，以及(E)超高压和低温磁力显微镜(与巴萨尔大学合作)，以及扫描电子和透射电子显微镜。在这些小尺寸的阵列上测量应变和ME耦合系数将为磁性薄膜器件的可靠加工提供重要信息。此外，磁点将模拟多晶材料中的颗粒行为，其中晶界提供了一些晶内外延失配应变的缓解。%这项研究在与自旋电子学和磁性随机存取存储器的新技术相关的科学进步方面具有极大的潜力。*

0105423O'HandleyNew, powerful ME-coefficient measurement techniques are used to study the effects of strain and dislocations in epitaxial magnetic nano-dots. The effects of limited lateral dimensions on strain relief and on ME effects are examined by using interferometric lithography to make highly-regular patterned arrays of magnetic dots and ovals having lateral feature sizes down to 25 nm and thickness from 2 to 20 nm. The program focuses on epitaxial Ni80 Fe20 and cobalt films on Cu-buffered Si (001), materials important for many magnetic thin film applications. The characterization of the film and dot arrays makes use of (a) synchrotron x-ray diffraction at BNL to determine strain, (b) torque magnetometry to characterize magnetic anisotropy, (c) vibrating sample magnetometry to determine saturation magnetization and Curie temperature, (d) differential capacitance measurements of first-order and second-order ME coupling coefficients, as well as (e) UHV and cryogenic magnetic force microscopy (in collaboration with the University of Basal), and scanning electron and transmission electron microscopy. Strain and ME coupling coefficient measurements on arrays at these small dimensions will provide important information for reliable processing of magnetic thin film devices. Further, the magnetic dots will mimic the behavior of grains in polycrystalline materials where grain boundaries provide some relief of intra-grain epitaxial misfit strain. %%%This study has excellent potential for advances in science with relevance to new technology in spintronics as well as magnetic random access memories.***