A time-resolved exploration of topological magnetic systems

点击翻译按钮获取中文摘要

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).