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arXiv 1712.03387cond-mat.mes-hall
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单晶镍纳米线中的周期性手征磁畴

Periodic chiral magnetic domains in single-crystal nickel nanowires

Jimmy J. Kan, Marko V. Lubarda, Keith T. Chan, Vojtech Uhlir, Andreas Scholl, Vitaliy Lomakin, Eric E. Fullerton

摘要:

我们报告了~0.2 × 0.2 × 8 μm单晶Ni纳米线畴结构的实验和计算研究。通过热化学气相沉积技术在非晶SiOx涂覆的Si衬底上生长Ni纳米线,该技术导致高度取向的单晶结构。磁电阻测量的Ni纳米线表明,在零场的平均磁化点主要偏离NW长轴。X射线光电子显微镜图像显示出沿纳米线表面的良好定义的周期性磁化图案,其周期为λ = 250 nm。有限元微磁学模拟表明,在剩磁下,可以获得周期与实验观测值(λ = 240 nm)非常接近的振荡磁化结构。这种磁化配置涉及沿NW的长度分布的交替手性涡旋域的周期性阵列。涡旋的形成归因于单晶Ni NW系统的立方各向异性及其减小的结构尺寸。周期性交替的手征涡旋态是拓扑保护的亚稳态,类似于薄条中的360°畴壁阵列。模拟结果表明,其他reflections状态也是可能的,这取决于现场的历史。研究了材料特性和应变对涡斑的影响。结果表明,在减少立方各向异性涡不再是稳定的,而负的单轴各向异性和磁弹性效应的压缩双轴应变的存在下,有助于涡的形成。

英文摘要:

We report on experimental and computational investigations of the domain structure of ~0.2 x 0.2 x 8 μm single-crystal Ni nanowires (NWs). The Ni NWs were grown by a thermal chemical vapor deposition technique that results in highly-oriented single-crystal structures on amorphous SiOx coated Si substrates. Magnetoresistance measurements of the Ni NWs suggest the average magnetization points largely off the NW long axis at zero field. X-ray photoemission electron microscopy images show a well-defined periodic magnetization pattern along the surface of the nanowires with a period of λ = 250 nm. Finite element micromagnetic simulations reveal that an oscillatory magnetization configuration with a period closely matching experimental observation (λ = 240 nm) is obtainable at remanence. This magnetization configuration involves a periodic array of alternating chirality vortex domains distributed along the length of the NW. Vortex formation is attributable to the cubic anisotropy of the single crystal Ni NW system and its reduced structural dimensions. The periodic alternating chirality vortex state is a topologically protected metastable state, analogous to an array of 360° domain walls in a thin strip. Simulations show that other remanent states are also possible, depending on the field history. Effects of material properties and strain on the vortex pattern are investigated. It is shown that at reduced cubic anisotropy vortices are no longer stable, while negative uniaxial anisotropy and magnetoelastic effects in the presence of compressive biaxial strain contribute to vortex formation.

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