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Enhanced Gilbert damping and role of metallic interfaces in large-angle spin precession

Enhanced Gilbert damping and role of metallic interfaces in large-angle spin precession. Single Fe layer. Double Fe layer. Exciting the magnetization. Au 10 layers. Au 10 layers. Epitaxial growth on GaAs(001) FMR characterization: damping a = 0.004 also measured anisotropies

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Enhanced Gilbert damping and role of metallic interfaces in large-angle spin precession

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  1. Enhanced Gilbert damping and role of metallic interfaces in large-angle spin precession Single Fe layer Double Fe layer Exciting the magnetization Au 10 layers Au 10 layers Epitaxial growth on GaAs(001) FMR characterization: damping a = 0.004 also measured anisotropies MOKE hysteresis loop magnetized in-plane [110] very soft! (HC = 12 Oe) Fe 10 or 15 layers Fe 15 layers constant current alignment parallel to field pulsed current (5 ps) precessional switching GaAs Au 40 layers Fe 40 layers • 4-fold wins over uniaxial: • easy-axis rotated ~45° • pattern more complicated GaAs The magnetic field pulse Magnetic imaging SEMPA images 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 top layer 15 ML Fe huge pattern is consistent with low anisotropy bottom layer 40 ML Fe SEMPA images of M (SEM with Polarization Analysis) one magnetic field pulse 10 ML Fe / GaAs (001) Generated by relativistic electron bunch at the Final Focus Test Beam of the Stanford Linear Accelerator M0 50 mm Peak field of 7.5 Tesla 10 mm away from center, falling off with 1/R 1 mm 50 mm 50 mm Relaxation Dynamic motion of M Conclusions After field pulse: damping causes dissipation of energy during precession fit using LLG equation: anisitropies same as FMR but damping a = 0.017 4x larger in-plane M • field pulse lifts M out of plane, deposits energy as demagnetizing field • precession switches M • relaxation by damping • Landau-Lifshitz-Gilbert: • Strong, ultrashort field pulse excites magnetization precession and relaxation • Ultrathin Fe layer: damping 4x larger than in FMRpossibly due to spin-currents across interface into paramagnet (enhanced for large-angle precession)Tserkovnyak, Brataas, BauerPhys Rev Lett 88, 117601 and B 66, 060404 (2002) • Fe double layer: complex patterndynamic exchange coupling via spin currents?Heinrich et al., Phys Rev Lett 90, 187601 (2003) M H lines of constant (initial) torque MxH (energy barrier for switching: KU)

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