| AVS 62nd International Symposium & Exhibition | |
| Magnetic Interfaces and Nanostructures | Tuesday Sessions |
| Session MI-TuM |
| Session: | Oxides, Fluorides, and Spin Structures |
| Presenter: | Stefano Bonetti, Stockholm University, Sweden |
| Authors: | S. Bonetti, Stockholm University, Sweden R. Kukreja, Stanford University Z. Chen, Stanford University F. Macia, Universitat de Barcelona, Spain J.M. Hernandez, Universitat de Barcelona, Spain A. Eklund, KTH Royal Institute of Technology, Sweden D. Backes, New York University J. Frisch, SLAC National Accelerator Laboratory Y. Acremann, Laboratorium für Festkörperphysik, ETH Zürich, Switzerland J. Katine, HGST G. Malm, KTH Royal Institute of Technology, Sweden S. Urazhdin, Emory University A.D. Kent, New York University Ohldag, SLAC National Accelerator Laboratory J. Stöhr, SLAC National Accelerator Laboratory H.A. Dürr, SLAC National Accelerator Laboratory |
| Correspondent: | Click to Email |
In this talk, I will describe the new scanning x-ray transmission microscope instrument that we recently built at the Stanford Synchrotron Radiation Lightsource (SSRL), at the SLAC National Accelerator Laboratory. In a single experiment, we are now able to measure extremely small magnetic, elemental and chemical signals at the nanoscale (with 35 nm resolution), in buried layers. We can also achieve a temporal resolutions of 50 ps, and synchronize our instrument to a microwave generator in order to detect excitations of up to 10 GHz in frequency. In order to show the capabilities of our technique, I will present two of our most recent results.
At first, I will discuss our successful attempt to directly image the injection of spins from a thin film ferromagnet into a non-magnetic Cu layer, when a bias current is fed through the ferromagnet/non-magnet interface. The elemental and chemical specificity of x-rays allows us to distinguish spin accumulation on Cu atoms located at the interface from those within the bulk of the Cu film. Spin accumulation in the film gives rise to an average transient magnetic moment per Cu atom of 3×10−5 μB around the Fermi level, which we explain using Mott’s two current model. We also find a greatly enhanced transient moment on the Cu interface atoms, which we attribute to enhanced spin dependent scattering via localized interface states.
Then, I will present the first time-resolved x-ray images of the spin-wave soliton generated by spin-torque when a spin-polarized current is injected from a nano-contact into an extended magnetic layer, a 5-nm thick permalloy (Ni80Fe20) film. The circular polarization of the photons, tuned at the resonant L3 absorption edge of Ni, allows for selectively probing the dynamics of the magnetization in the film. By synchronizing the spin waves oscillations to the RF cavity of the synchrotron, we are able to create a phase resolved map of the magnetic excitation, i.e. a spin-wave "movie." The unprecedented combined temporal and spatial resolution, and the ability to look through the thick metal electrodes that provide the current necessary to excite the dynamics, reveal intriguing details of the spin-wave dynamics. In particular, we observe the emergence of a novel localized spin-wave soliton with a nodal line, i.e. with p-like symmetry, qualitatively different from the predicted solitonic excitation with essentially cylindrical symmetry (i.e. s-like).
Our studies provide a deeper understanding of magnetism at the nanoscale, and highlight the importance of nanoscale time-resolved techniques to tackle the challenges of modern magnetism.