Experimental Investigation Of Spin Dynamics In Ferromagnetic Film By Ultrafast Optical Technique

With the rapid development of information science,spin is expected to break through the limitations of charge in electronic devices as one of the intrinsic properties of electrons.Therefore,spintronics,which studies various application functions such as data storage,logical operation and quantum computing through regulating and manipulating spin,came into being.Magnetic materials are constantly being proposed as higher performance requirements as spin information storage media during the research process.Driven by high-speed and low-cost information storage,in order to achieve faster control of magnetic moment motion,the study of the magnetic moment in magnetic materials on ultra-fast scales has attracted the attention of researchers in the field of spintronics.Ultrafast pulsed laser can stimulate the phenomenon of ultrafast demagnetization and recovery of magnetization and precession of magnetic moment when the magnetic material rapidly reaches the non-equilibrium state.However,our current physical connotation of the spin behavior of magnetic materials cannot be systematically understood.Therefore,in order to complete the theoretical research and practical application as a storage material,we carried out specific experiments to study the spin dynamics process of ultrafast pulsed laser excited magnetic materials.In addition,two-dimensional van der Waals(2D vd W)magnetic materials have been observed experimentally due to the many quantum phenomena in which quantum-restricted atomic sizes are generated,and thus have attracted wide attention of researchers.In the process of understanding the behavior of electrons in the system and improving the application value of magnetic materials,the study of various related physical properties such as optics,magnetism and electrostatic regulation is of great significance.The main contents of this paper are:(1)Based on the pump-detection magneto-optical technique,alow-temperature and high-sensitivity time-resolved Faraday rotation(TRFR)detection system was established.The platform achieves a sub-picosecond time resolution with a femtosecond pulsed laser.The focused spot can achieve a spatial resolution of approximately 2 ?m and the angle between the sample surface and the magnetic field can be arbitrarily changed.Ultrafast spin kinetics measurements of Co Fe B/Mg O ferromagnetic films with perpendicular anisotropy were also carried out at room temperature using the platform to verify the reliability and space-time resolution of the system.(2)Using the time-resolved two-color pump-detecting Faraday rotation detection platform,the system measured the spin-dynamic process excited by laser in Co Fe B/Mg O ferromagnetic thin film structure,and observed the signal of ultra-fast demagnetization and spin precession.The effects of different pump energy densities,applied magnetic field strengths and angles on spin precession behavior and Gilbert damping are investigated.The experimental results show that the magnetization precession frequency is in agreement with the theoretical calculation based on the Landau-Lifshitz-Gilbert(LLG)equation.In addition,the spatial distribution of the sample demagnetization signal was scanned,and the dynamics of the magnetic domain were observed.(3)The static magnetic properties and ultra-fast dynamics of 2D vd W magnetic materials were studied.The Gilbert precession in the ultrafast kinetics process was measured,and the LWG equation and its derivative formula were used to fit it well and the damping constant of the material was obtained.