Optically-induced ultrafast spin dynamics study on perpendicular magnetic anisotropy materials = 펨토초 레이저로 유도된 수직 자성 물질의 초고속 스핀 동역학 연구

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In this thesis, in order to study ultrafast spin dynamics of promising perpendicular magnetic anisotropy materials, we have accomplished two types of optically-induced time-resolved magneto-optical Kerr experiments based on Ti:sapphire femtosecond laser. One type is the ultrafast magnetic field-induced experiment and the other type is the femtosecond laser-induced experiment. For the field-induced experiment, with the photolithography technique, we have carefully fabricated the $[Co/Pd]_5$ multilayer dot pattern on the photoconductive switch pattern structure which can generate a ultrafast current pulse. Unexpectedly, we could not observe any precessional behavior of Co/Pd sample. Assuming that this overdamped-like motion was attributed to its intrinsic many energy dissipation channels, the Gilbert damping constant, $\alpha$ was estimated to be much larger than one. However, because extrinsic possibilities such as the weak magnetic pulse field and the corrosion of the sample during the lift-off process cannot be excluded, further study needs to be progressed. For the laser-induced study with completeness, two different samples have been prepared. The amorphous $Tb_{35}Fe_{65}$ alloy film was aimed at the fundamental study on the subpicosecond time regime and the $L1_0$ -ordered $Fe_{50}Pt_{50}$ alloy film has been made with the application point of view. In case of $Tb_{35}Fe_{65}$ sample, interestingly enough, steplike demagnetization has been observed even at a subpicosecond when electrons are not in a thermal equilibrium state. With an extended three-temperature model simulation, we have identified that unusual ultrafast demagnetization is attributed to an energy transfer from a nonthermal electron to a spin system. For the application point of view, we have studied spin precessional dynamics of $L1_0$- ordered $Fe_{50}Pt_{50}$ at a few tens of picosecond time scale. Although its extremely tiny precessional signal, we obviously have detected and anlayz...
Shin, Sung-Chulresearcher신성철researcher
한국과학기술원 : 물리학과,
Issue Date
418650/325007  / 020045066

학위논문(박사) - 한국과학기술원 : 물리학과, 2010.2, [ viii, 66 p. ]


time-resolved; pump-probe; optically-induced; ultrafast spin dynamics; 초고속 스핀 동역학; 시간 분해능; 펌프 프로브; 레이저 유도

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