[论文解读] Experimental observation of magnetic bobbers for a new concept of magnetic solid-state memory

Fengshan Zheng, Filipp N. Rybakov+12 more|arXiv (Cornell University)|Jun 14, 2017

Magnetic properties of thin films参考文献 37被引用 101

一句话总结

Direct observation of chiral bobbers coexisting with skyrmions in FeGe thin films using off-axis electron holography, proposing a binary data encoding scheme for magnetic solid-state memory without fixed inter-carrier spacing.

ABSTRACT

The use of chiral skyrmions, which are nanoscale vortex-like spin textures, as movable data bit carriers forms the basis of a recently proposed concept for magnetic solid-state memory. In this concept, skyrmions are considered to be unique localized spin textures, which are used to encode data through the quantization of different distances between identical skyrmions on a guiding nanostripe. However, the conservation of distances between highly mobile and interacting skyrmions is difficult to implement in practice. Here, we report the direct observation of another type of theoretically-predicted localized magnetic state, which is referred to as a chiral bobber (ChB), using quantitative off-axis electron holography. We show that ChBs can coexist together with skyrmions. Our results suggest a novel approach for data encoding, whereby a stream of binary data representing a sequence of ones and zeros can be encoded via a sequence of skyrmions and bobbers. The need to maintain defined distances between data bit carriers is then not required. The proposed concept of data encoding promises to expedite the realization of a new generation of magnetic solid-state memory.

研究动机与目标

• 利用局部磁状态来实现超越传统斯格明子的记忆体系结构的动机。
• 在薄膜手性磁体中实验 Demonstrate that chiral bobbers can coexist with skyrmions 直观？
• Demonstrate experimentally that chiral bobbers can coexist with skyrmions in thin-film chiral magnets.
• Quantify how field, thickness, and geometry affect the stability and readout signals of bobbers and skyrmions.
• Propose a data-encoding scheme that uses a sequence of skyrmions and bobbers as binary bits.
• Assess the feasibility of a high-density, low-energy, mechanical-part-free magnetic memory approach.

提出的方法

• 进行微磁模拟以预测 SkTs 与 ChBs 的共存与场依赖相位偏移。
• 在透射电子显微镜中使用离轴全息法测量磁相位偏移，指示面内磁化分量。
• 用 E = ∫(E_ex + E_DMI + E_Z + E_d) dV 射能来建模能量贡献，参数为 A、D、Ms。
• 对 FeGe 进行 L_D ≈ 70 nm 的模拟，以探讨纳米条中的 SkT 与 ChB 配置。
• 在大致 95 K 温度下，对楔形样品和固定厚度 FeGe 样品在外场（200–400 mT）下进行实验。
• 将实验的相位对比数据与微磁预测相关联，以识别 SkT 与 ChB。

实验结果

研究问题

• RQ1 手性浮标（ChBs）在薄膜手性磁体中是否存在且能否与斯格明子（SkTs）共存？
• RQ2 在何种场强和厚度范围内，SkTs 与 ChBs 能共存并可通过晕相位信号分辨？
• RQ3 SkTs 与 ChBs 的相移信号如何随所施加的磁场和薄膜厚度而变化？
• RQ4 是否可以通过以 SkTs 与 ChBs 序列编码二进制位来实现数据存储方案？
• RQ5 ChB-SkT 共存对潜在类赛车道记忆的读写擦除有何影响？

主要发现

• 直接观察到 ChBs 在 FeGe 薄膜中与 SkTs 共存，使用离轴电子全息法。
• 相移信号在一系列场中区分 SkTs（较强）与 ChBs（较弱），在大约 250–350 mT 区间有清晰分离。
• 在楔形样品中，两个不同对象类型产生对比鲜明的相移，可区分 SkTs 与 ChBs。
• 在 300 mT 时，ChB 对比度约为 SkT 对比度的一半，与理论预测一致。
• ChB 信号在特定场窗和样品厚度范围内保持，而在较高场（在 95 K 时约 400 mT）ChBs 会崩解。
• 共存支持一种数据编码概念，即以 SkTs 与 ChBs 的交替来表示 1 与 0 的流，不再需要固定的粒子间距。