Study on magnetization reversal process and magnetic property manipulation in a carrier- induced ferromagnetic semiconductor

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We have studied the magnetization reversal process and magnetic property manipulation in a carrier- induced ferromagnetic semiconductor Ge_<1-X>Mn_XTe, and obtained the following results.1.Magneto-resistances (MRs) have been measured in Ge_<1-X>Mn_XTe having various carrier concentrations and Mn compositions. The MR behavior for the rotating field has been fitted by the simulation assuming the pinning field distribution. The larger pinning field was obtained in the sample indicating the larger negative MR in the high magnetic field region. This suggests that the inhomogeneity of the local spins, which hindered the magnetization rotation, would be the formation of the magnetic polarons.2.Ge_<1-X>Mn_XTe fine wires having 10〜0.8μm have been fabricated with the electron beam lithography technique. The tilt of the magnetization from the longitudinal direction at zero field was suppressed with decreasing wire width in the MR curve when the magnetic field applied along the longitudinal direction for the sample with 400nm-thick and Mn composition x=0.25. However, the obvious difference in the MR curves for the longitudinal and transverse directions was not observed. Considering the results in section 1 and 3, the inhomogeneous magnetization reversal in the local regions seems to be dominant in the studied samples.3.Magnetization reversal properties have been investigated with the micromagnetic computation. The material parameters were estimated from the experimental results. For the 100nm-thick film, the generation of π wall was observed in the wires below 0.8μm width. For the 0.6μm-width wire, the amplitude of magnetization reversal field decreased with the film thickness above 200nm due to the domain wall nucleation.4.MnTe(antiferromagnetic)/Ge_<1-X>Mn_XTe(ferromagnetic) semiconductor coupled films were grown on SrF_2 substrate by molecular-beam epitaxy. The loop shift of 50 Oe was observed in the hysteresis curve at 5K.