Perpendicular Exchange Bias Effect And Ultrafast Spin Dynamics On CoFeB/Pt/IrMn Multilayers

The magnetic thin films with exchange bias effect play an important role in the magnetic electronic device,which make the exchange bias effect have important research significance.In this paper,perpendicular exchange bias effect and ultrafast spin dynamics of Pt/CoFeB/Pt/MnIr stucture were studied by VSM measurement and Time-resolved Magneto-optical Kerr Effect.And the coherent acoustic phonon excited by the femtosecond laser pulse in this magnetic thin film is explored.This thesis includes the following sections:1.The static magnetic and ultrafast spin dynamics of Pt/CoFeB/Pt/MnIr magnetic thin films with perpendicular exchange bias effect were studied.Firstly,the influence of Pt interlayer thickness,MnIr antiferromagnetic layer thickness and annealing under magnetic field on the exchange bias is investigated and the maximum exchange bias field is 202Oe.Secondly,we studied the effect of laser pulse fluence on the exchange bias field.We observed the process that the exchange bias field disappeared when the laser pulse arrived but recovered within 200 fs because of heating effect.And it is considered that this process is related to the electron temperature.Then we obtained the effects of the bias field and anisotropic field on Gilbert's damping constant for different laser fluence.2.The interaction between the femtosecond laser pulse and the MnIr layer in the magnetic thin film excites the coherent acoustic phonon with an initial phase of 90 ° and a propagation velocity of 4290 m/s.The vibration frequency of the acoustic phonon is independent of the laser energy density and is inversely proportional to the total thickness of the magnetic thin film.The mechanism of the coherent acoustic phonon may be that the electron temperature in the magnetic thin film increases sharply induced by femtosecond laser pulse,then an decreasing electron temperature gradient with increasing depth is generated instantaneously by the absorption of the laser which lead to the lattice oscillate coherently in the depth direction.