Understanding magnetism in ferromagnetic metal/semiconductor (FM/SC) heterostructures is important to the development of the new-generation spin field-effect transistor. Here, we report an element-specific X-ray magnetic circular dichroism study of the interfacial magnetic moments for two FM/SC model systems, namely, Co/GaAs and Ni/GaAs, which was enabled using a specially designed FM1/FM2/SC superstructure. We observed a robust room temperature magnetization of the interfacial Co, while that of the interfacial Ni was strongly diminished down to 5 K because of hybridization of the Ni d(eg) and GaAs sp(3) states. The validity of the selected method was confirmed by first-principles calculations, showing only small deviations (<0.02 and <0.07 μB/atom for Co/GaAs and Ni/GaAs, respectively) compared to the real FM/SC interfaces. Our work proved that the electronic structure and magnetic ground state of the interfacial FM2 is not altered when the topmost FM2 is replaced by FM1 and that this model is applicable generally for probing the buried magnetic interfaces in the advanced spintronic materials..

We present the room temperature magnetization hysteresis loop measurements of a triangularly shaped Fe64Ni36 dot array with the feature size down to 30 nm using magneto-optical Kerr effect. An in-plane anisotropic magnetization reversal and an enhanced coercivity have been observed in these magnetic dots. In combining with micromagnetic calculations, we found that the magnetization process follows two steps, the rotation of the top corner and the switching of the bottom base, respectively, controlled by the nanometer scale local magnetic shape anisotropy, and the thermal activation is negligible even in this length scale.

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Optically induced ultrafast spin dynamics in nanoscale single crystal Fe dot arrays have been investigated using time-resolved magneto-optical Kerr effect (MOKE) pump-probe measurements. An ultrafast demagnetization process has been found to occur in the first 400fs after the excitation with the femtosecond laser pulses for both the patterned dot arrays and the continuous film. While in the continuous Fe film the magnetization recovers monotonically with no precession, an optically induced spin precession has been observed in the patterned dot array with the precession frequency and the damping dependent on bias field strength. This result demonstrates that the modified magnetic anisotropies, as shown by the static focused MOKE measurements, in the patterned nanostructures can give rise to the optically induced spin precession.