Magnetization dynamics in all-optical pump-probe experiments: spin-wave modes and spin-current damping

摘要: In the field of spintronics, future development demands a new insight into magnetization relaxation processes in sub nanosecond regime. With time resolution inherent, femtosecond laser pulses all-optical pump-probe experiments can be used to study basic constants ultrafast demagnetization, magnetic precessional modes and energy dissipation processes. This thesis investigates dynamics thin nickel samples regarding coherent incoherent The intense 80fs pulse an amplified Ti:Sapphire oscillator is both excite sample monitor using magneto-optical Kerr effect.Ultrafast demagnetization shortly after excitation by pump investigated varying fluencies external field. Delayed remagnetization for highly excited on timescales few picoseconds observed. describes evolution high spin waves with lower k-vectors.Various are observed upon depending thickness ferromagnet. Kittel mode present all films. Standing wave up 3rd order thicker than optical penetration depth laser. dipole dominate spectra much depth. Frequency dispersion relations these reveal material (anisotropy constant, exchange constant). Gilbert damping parameter which assigned each mode.The ferromagnetic/nonmagnetic double layers means extrinsic spin-current induced damping. Two-magnon scattering increases rough interface. precession ferromagnetic layer pumps spins nonmagnetic opens channel. additional currents inversely proportional only thinner 10nm. efficiency pumping determined accumulation sink. Spin sink 5nm dysprosium, palladium or chromium studied within induce strong increase parameter.