Berlin 2018 – scientific programme
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MA: Fachverband Magnetismus
MA 2: Focus Session: Nanomagnetism in the x-ray spotlight
MA 2.3: Invited Talk
Monday, March 12, 2018, 10:30–11:00, H 1012
Direct observation of magnetic droplet solitons — •Martina Ahlberg1, Sunjae Chung1,2,3, Q. Tuan Le1,2, Ahmad A. Awad1, Markus Weigand4, Iuliia Bykova4, Roman Khymyn1, Mykola Dvornik1, Hamid Mazraati2, Afshin Houshang1, Sheng Jiang2, T. N. Anh Nguyen1,2,5, Eberhard Goering4, Gisela Schütz4, Joachim Gräfe4, and Johan Åkerman1,2 — 1University of Gothenburg, Gothenburg, Sweden — 2KTH Royal Institute of Technology, Kista, Sweden — 3University Uppsala, Uppsala, Sweden — 4Max Planck Institute for Intelligent Systems, Stuttgart, Germany — 5Vietnam Academy of Science and Technology, Hanoi, Vietnam
The magnetic droplet is a localized excitation found in uniaxial ferromagnets where a polarized current provides sufficient spin transfer torque to counteract the inherent damping. This dissipative soliton was first detected in nanocontact spin torque oscillators (NC-STO). The droplet is created underneath the contact and is predicted to have a reversed core where the spins precess at angles almost antiparallel to the initial state. However, the first images of a droplet revealed much smaller precession angles.
In this work we use all-perpendicular NC-STOs and image the spin wave excitation by X-ray microscopy. We observe a fully reversed droplet core, in accordance with theory, while the droplet diameter is twice as big as the expected value. Micromagnetic simulations show that the origin of the enlargement is current-in-plane Zhang-Li torque adding an outward pressure on the droplet perimeter. We also image the evolution of the magnetic state as a function of current and field.