Manipulation of skyrmions with tailored acoustic potentials

磁性skyrmions是纳米级的粒子状自旋结构，具有非零拓扑电荷，出现在一些凝聚态物质系统中，如磁性多层材料。大约在十年前，有人预测它们可以用少量的电流沿着磁线传输，这导致了在磁存储器和非冯·诺伊曼计算体系结构中使用它们的各种建议。然而，在实践中，skyrion的运动受到晶界和磁性材料中的其他缺陷的阻碍，这意味着所需的电流远远超过预期，导致能量浪费主要以焦耳加热的形式出现。在这个项目中，我们不再尝试进一步改进磁性材料，而是完全避免使用电流，而是使用表面声波（saw）来操纵skyrmions。博士项目的目的是进一步研究saw对skyrmions的操纵，主要是通过实验，但辅以微磁模拟。我们目前研究的合成反铁磁（SAF）多层材料包含比铁磁体更小的skyrmions，并且有望用于低功耗操作，这是本项目将主要研究的SAF材料。该项目的主要挑战是制造GHz频率的SAW换能器，用于操纵这些纳米尺度的skyrmions，并检测skyrmions的响应。Royce沉积系统和凝聚态物质组内的磁性表征工具将用于沉积和研究SAF多层材料。SAW换能器将在该大学的Wolfson洁净室制造。结构表征和显微镜将使用布拉格中心的设备进行。同步加速器技术将补充利兹现有的磁成像技术。

Magnetic skyrmions are nanoscale, particle-like swirling spin textures with a non-zero topological charge that appear in some condensed matter systems such as magnetic multilayers. About a decade ago it was predicted that they could be transported along a magnetic wire using small amounts of electrical current, and this has led to a variety of proposals for their use in magnetic memory and non-von Neumann computing architectures. However, in practice skyrmion motion is hindered by grain boundaries and other imperfections in the magnetic material, meaning that far more current is needed than predicted, leading to energy wastage mainly in the form of Joule heating. Rather than try to refine the magnetic material any further, what we will do in this project is avoid using currents altogether, and instead use surface acoustic waves (SAWs) to manipulate skyrmions. The aim of the PhD project is to further investigate the manipulation of skyrmions by SAWs, mainly by experiment, but complemented by micromagnetic simulations. Synthetic antiferromagnetic (SAF) multilayers that we currently study contain skyrmions that are even smaller than those in ferromagnets, and hold promise for low-power manipulation, and it is SAF materials that will mainly be investigated in this project. The main challenges of the project are to fabricate GHz frequency SAW transducers for the manipulation of these nanoscale skyrmions and to detect the skyrmion response. The Royce Deposition System and magnetic characterisation tools within the Condensed Matter Group will be used to deposit and study the SAF multilayers. SAW transducers will be fabricated in the university's Wolfson cleanroom. Structural characterisation and microscopy will be performed using Bragg Centre facilities. Synchrotron techniques will complement the magnetic imaging available in Leeds.