Enhanced Gilbert damping and role of metallic interfaces in large-angle spin precession Christian Stamm, Ioan Tudosa, Frank King, Hans-Christof Siegmann, Joachim Stöhr Stanford.
Download ReportTranscript Enhanced Gilbert damping and role of metallic interfaces in large-angle spin precession Christian Stamm, Ioan Tudosa, Frank King, Hans-Christof Siegmann, Joachim Stöhr Stanford.
Enhanced Gilbert damping and role of metallic interfaces in large-angle spin precession Christian Stamm, Ioan Tudosa, Frank King, Hans-Christof Siegmann, Joachim Stöhr Stanford Synchrotron Radiation Laboratory and Stanford Linear Accelerator Center, Stanford, USA Georg Woltersdorf and Bret Heinrich, Simon Fraser University, Burnaby, Canada Andreas Vaterlaus, Swiss Federal Institute of Technology, Zurich, Switzerland Exciting the magnetization Single Fe layer Au 10 layers Fe 10 or 15 layers constant current Epitaxial growth on GaAs(001) GaAs alignment parallel to field FMR characterization: damping a = 0.004 also measured anisotropies pulsed current (5 ps) MOKE hysteresis loop magnetized in-plane [110] very soft! (HC = 12 Oe) precessional switching The magnetic field pulse 4 60 GaAs • pattern more complicated bottom layer 40 ML Fe 0 40 80 4-fold wins over uniaxial: • easy-axis rotated ~45° 50 mm M0 2 20 Fe 40 layers top layer 15 ML Fe huge pattern is consistent with low anisotropy (SEM with Polarization Analysis) one magnetic field pulse 10 ML Fe / GaAs (001) 0 Au 40 layers SEMPA images SEMPA images of M 6 -20 Au 10 layers Fe 15 layers Magnetic imaging 8 B [Tesla] Generated by relativistic electron bunch at the Final Focus Test Beam of the Stanford Linear Accelerator Double Fe layer 100 t [ps] Peak field of 7.5 Tesla 10 mm away from center, falling off with 1/R 1 mm 50 mm Relaxation Dynamic motion of M in-plane M M After field pulse: • field pulse lifts M out of plane, deposits energy as demagnetizing field damping causes dissipation of energy during precession • precession switches M 6 • relaxation by damping fit using LLG equation: anisitropies same as FMR but damping a = 0.017 4x larger 4 E/Ku H lines of constant (initial) torque MxH 50 mm • Landau-Lifshitz-Gilbert: 1 dM 1 a dM MH M dt M dt 2 10 ML Fe 15 ML Fe 0 0 1 2 3 Number of precessions 4 (energy barrier for switching: KU) Conclusions • Strong, ultrashort field pulse excites magnetization precession and relaxation • Ultrathin Fe layer: damping 4x larger than in FMR possibly due to spin-currents across interface into paramagnet (enhanced for large-angle precession) Tserkovnyak, Brataas, Bauer Phys Rev Lett 88, 117601 and B 66, 060404 (2002) • Fe double layer: complex pattern dynamic exchange coupling via spin currents? Heinrich et al., Phys Rev Lett 90, 187601 (2003)