Browsing by Author "Wang, Jigang"

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    Magneto-optical Kerr effect and magnetic circular dichroism in ferromagnetic indium-manganese-arsenic/gallium-antimony heterostructures
    (2002) Wang, Jigang; Kono, Junichiro
    This thesis describes a Magneto-Optical Kerr Effect (MOKE) and Magnetic Circular Dichroism (MCD) study of ferromagnetism in III-V magnetic semiconductor heterostructures. This work was initiated due to the much recent interest in spin-related phenomena in semiconductors. The discovery of carrier/light-induced ferromagnetism in InMnAs-based heterostructures has opened up new possibilities for spin-based multifunctional devices that will integrate photonics, magnetics and microelectronics. However, an experimental demonstration of direct ultrafast optical manipulation of spins/magnetic order in this system has not been reported, although it is considered to be a crucial step towards pico- or femto-second operation of information encoded in the spin degree of freedom. In addition, the origin of ferromagnetism is still a subject of debate. To address these issues, we have developed an experimental setup for performing continuous-wave (CW) and time-resolved light-induced MOKE/MCD experiments. Our data clearly demonstrate that magnetic properties, e.g., coercivity and remanent magnetization, can be optically controlled in an ultrafast manner (∼ ps). The experimental results of CW and two-color time-resolved MOKE/MCD measurements are presented. Finally, the mechanism of the ultrafast MOKE response is discussed in terms of transient photo/carrier-induced modifications of exchange interaction and domain wall energy.
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    Ultrafast magneto-optical spectroscopy of (III,manganese)V ferromagnetic semiconductors
    (2005) Wang, Jigang; Kono, Junichiro
    This thesis describes magneto-optical processes in ferromagnetic (III,Mn)V semiconductors and their heterostructures induced by femtosecond laser pulses. Two-color ultrafast magneto-optical spectroscopy has been developed, which allows us to observe a rich array of dynamical phenomena that are absent in traditional nonmagnetic semiconductors or metallic/insulating magnets. We isolate several distinct temporal regimes in spin dynamics, interpreting the fast (< 1 ps) dynamics as spin heating through sp-d exchange interaction between photo-carriers and Mn ions while the ∼100 ps component as a manifestation of spin-lattice relaxation. Charge carrier and phonon dynamics were also carefully studied, showing an ultrashort charge lifetime of photoinjected electrons (∼ 2 ps) and propagating coherent acoustic phonon wavepackets with strongly probe energy dependent oscillation period, amplitude and damping.