All-optical Method To Study The Semi-metallic Co <sub> 2 </ Sub> Of Feal <sub> 0.5 </ Sub> Si <sub> 0.5 </ Sub> Film Spin Dynamics

With the development of modern society, it has been greatly increased for the requirement of information by the human being. So there is the same quantity requirement of the storage media for the information. The technologies of different storage media have been developed in highway since 90s last century, and so did the traditional storage media-magnetic thin film. Spintronics has become very important research topic for its irreplaceable position for fundamental mechanism of magnetic media. It became more and more difficult to learn the ultrafast process like magnetization reversal or precession of magnetic storage media by the conventional methods. With the development of femto-second (fs) laser technology, a time resolved optical pump-probe technique with magneto-optical Kerr effect (MOKE) can be used to study the ultrafast process like transient reversal of magnetization and the limit of magnetization reversal speed in magnetic system. The research was carried out with these backgrounds by the Time Resolved MOKE (TRMOKE) system, and the dissertation includes the following contents.Firstly, we carried out the research about magnetic damping absorption of Co based Heusler alloy Co2FeA10.5Si0.5(CFAS) thin films. The samples of Heusler alloy CFAS were treated in different annealing temperatures to realize different crystalline phase, from disordered A2 phase to completely ordered L2(1) phase. We investigated the magnetization precession of samples induced by the fs pump laser pulse. And we study magnetization precession with different applied fields. The magnetic damping characters could be gained with the fitting and description of Landau-Lifschitz-Gilbert motion function. The precession frequency and the chirp effect are found to depend on the magnitude of the measured magnetic field while the damping rate is independent of the measured magnetic field. The chirp effect is close to each other for L2(1) and B2-ordered CFAS films. The damping rate of the B2-ordered film is smaller than that of the L2(1) one.Secondly, we studied the simulation of ultrafast field cooling process of IrMn/CoFe bilayer exchange bias samples. For different thickness of antiferromagnetic(AFM) layer samples, we applied with different power of pump laser pulses and saturation magnetic field to simulate ultrafast field cooling process. The static MOKE loops were used to describe the spin state of ferromagnetic (FM) and AFM layers. It's realized that the state of FM/AFM coupling of exchange bias samples was adjusted by changing the directions of applied fields and power of pump laser pulse.