Dresden 2009 – scientific programme
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MA: Fachverband Magnetismus
MA 7: Spin-Dynamics/ Spin-Torque II
MA 7.9: Talk
Monday, March 23, 2009, 17:30–17:45, HSZ 04
Coherent switching of the vortex core polarization by monopolar magnetic field pulses — •Markus Weigand1, Michael Curcic1, Bartel Van Waeyenberge1, Arne Vansteenkiste3, Vitalij Sackmann1, Hermann Stoll1, Tolek Tyliszcak2, Georg Woltersdof4, Christian Back4, and Gisela Schütz1 — 1MPI f. Metallforschung, Stuttgart — 2ALS, Berkeley, USA — 3Ghent University, Belgium — 4Uni. Regensburg
Time-resolved imaging of vortex core reversal in 500nm large Permalloy Landau structures has been achieved by 'pump-and-probe' measurements at a scanning-transmission X-ray microscopy (STXM), combining <100 ps and ~30 nm time and lateral resolution. A fast data aquisition system recorded up to 1000 time frames simultaneously, capturing the entire excitation and relaxation cycle of the vortex core.
The vortex polarization could be switched by in-plane monopolar magnetic pulses as low as 5-15mT, depending on sample geometry. This was achieved by taking advantage of a 'resonance timing' of the rising and falling pulse edges of the excitation field pulse: Provided a correct adjustment of the pulse length, the vortex is accelerated by the rising edge as well as by the falling edge, causing a doubling of the gyration amplitude. When a critical velocity is reached, the vortex core switches.
The excitation and relaxation sequences as shown in our movies and the meassured switching thresholds agree well with micromagnetic simulations. Applications for current (spin torque) induced vortex core reversal will be addressed, too.