A time-resolved exploration of topological magnetic systems

到目前为止，传统的铁磁共振（FMR）已被广泛用于确定薄膜中的基本磁参数，使用共振频率（与内部和施加的磁场）和弛豫（由共振的阻尼确定）。此外，它已被用作内部动态skyrmion模式的间接识别，例如，顺时针和逆时针旋转模式或呼吸模式。然而，拓扑磁系统需要开发新的技术，直接访问其动态特性。X射线探测铁磁共振（XFMR）技术使我们能够通过X射线磁圆二色性（XMCD）研究元素选择磁化动力学。随时间变化的XFMR测量化学性质不同的层的自旋进动的振幅和相位。实验的挑战是旋进频率在GHz数量级，旋进锥角<1度。解决方案在于利用同步加速器的时间结构（约500 MHz）进行频闪测量。驱动自旋进动的射频（RF）场使用同步加速器的时钟与X射线脉冲同步。每个X射线脉冲都在周期中的同一点测量磁化锥。简而言之，XFMR结合了FMR和XMCD，分别作为泵浦和探测器。逆自旋霍尔效应（ISHE）是一个将自旋电流转换为电流的过程，可以在简单的铁磁/顺磁双层系统中系统地研究，其中由铁磁共振驱动的自旋泵浦将自旋电流注入顺磁层。本项目的目的是将联合收割机XFMR和ISHE结合起来，分别检测自旋泵的交流和直流分量。该项目的意义在于扩展Diamond和世界范围内其他同步加速器的自旋动力学表征能力，深入了解涌现场对拓扑磁性物体输运性质的影响。我们设想利用牛津物理学的综合独特能力（薄膜生长，FMR，ISHE），金刚石（XRD/XRR、SQUID、ISHE、FMR、XAS/XMCD/XMLD、XFMR）和RAL（MOKE），特别是位于Diamond的便携式八极磁体系统（POMS）终端站。该项目与EPSRC的研究领域“凝聚态物质：磁性和磁性材料"和"自旋电子学"。该项目是与钻石光源（Gerrit货车der Laan教授）的联合项目。

Until now, conventional ferromagnetic resonance (FMR) has been used extensively to determine fundamental magnetic parameters in thin films using resonance frequencies (related to internal and applied fields) and relaxation (determined by damping of the resonance). Further, it has been used as an indirect identification of the internal dynamic skyrmion modes, e.g., clockwise and anticlockwise gyration modes or breathing modes. However, topological magnetic systems require the development of new techniques that give direct access to their dynamical properties. The novel technique of X-ray detected FMR (XFMR) enables us to study the element-selective magnetization dynamics via X-ray magnetic circular dichroism (XMCD). Time-dependent XFMR measures both the amplitude and phase of the spin precession of chemically distinct layers. The experimental challenge is that the precession frequency is on the order of GHz and the precession cone angle is <1 degree. The solution lies in stroboscopic measurements utilizing the time structure of the synchrotron (approx 500 MHz). The radio frequency (RF) field that drives the spin precession is synchronized with the X-ray pulses using the clock of the synchrotron. Each X-ray pulse measures the magnetisation cone at precisely the same point in the cycle. In brief, XFMR combines FMR and XMCD as pump and probe, respectively.The inverse spin-Hall effect (ISHE) is a process that converts a spin current into an electric current and can be investigated systematically in simple ferromagnetic/paramagnetic bilayer systems, whereby the spin pumping driven by ferromagnetic resonance injects a spin current into the paramagnetic layer. The aim of the Project is to combine XFMR with ISHE, which detect the AC and DC components of the spin pumping, respectively. The significance of this Project is to expand the characterisation capabilities for spin dynamics at Diamond and other synchrotrons world-wide, giving insight into the effects of emergent fields on the transport properties of topological magnetic objects.We envision to make use of the combined unique capabilities of Oxford Physics (thin film growth, FMR, ISHE), Diamond (XRD/XRR, SQUID, ISHE, FMR, XAS/XMCD/XMLD, XFMR), and RAL (MOKE), and in particular the portable octupole magnet system (POMS) end station at Diamond.This project aligns with EPSRC's research areas "Condensed Matter: Magnetism and Magnetic Materials" and "Spintronics".This project is a joint project with the Diamond Light Source (Prof Gerrit van der Laan).