| Magnetic storage medium renewal is of great importance in magnetic storage technology. As practical magnetic storage media, magnetic thin films have attracted much attention. Time-resolved magneto-optical Kerr effect (TRMOKE) can be used to study the transient magneto-optical response and the speed limit of the reversal of magnetic domain. In this paper, we used TRMOKE to measure two kinds of magnetic films, and studied their ultrafast spin dynamics.This thesis includes the following sections:1. Two-step demagnetization is observed in the TRMOKE curve of TbFeCo magnetic films. The slow demagnetization time is of dozens of picosecond while the ultrafast demagnetization time is of hundreds of femtosecond. As the Tb contents increasing, demagnetization become weaker. Two-step demagnetization can be explained by four-temperature model. The interaction between the photo-excited electron and the spin of FeCo leads to the fast demagnetization while the interaction among lattice, FeCo spin and Tb spin results in the slow demagnetization..2. We investigated static magnetism and ultrafast spin dynamics in MnIr/[CoFeB/Pd]N magnetic films. The exchange bias arises until the thickness of MnIr is 2.4 nm. Gilbert damping is observed in TRMOKE curves of MnIr/[CoFeB/Pd]N magnetic films and well fitted by LLG equations. By analyzing Gilbert damping of samples with different underlayer, we discover the linear relationship between Gilbert damping and exchange coupling energy. |
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