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

本文研究了载流子诱导铁磁半导体Ge_ Mn_XTe的磁化反转过程和磁性能调控<1-X>，得到了以下结果：1.测量了<1-X>不同载流子浓度和Mn组分的Ge_ Mn_XTe的磁电阻。在假定钉扎场分布的情况下，通过模拟拟合了旋转场的MR行为。在样品中获得了较大的钉扎场，表明在高磁场区具有较大的负MR。这表明局域自旋的不均匀性阻碍了磁化旋转，可能是磁极化子的形成。2.<1-X>用电子束光刻技术制备了10 μ m ~ 0.8μm的Ge_ Mn_xTe细线。当磁场沿着纵向施加时，对于厚度为400 nm、Mn组分x=0.25的样品，随着磁电阻曲线中线宽的减小，零场下磁化强度相对于纵向的倾斜被抑制。然而，纵向和横向的MR曲线没有观察到明显的差异。考虑到第1节和第3节的结果，在所研究的样品中，局部区域的非均匀磁化反转似乎占主导地位。3.利用微磁学计算研究了磁化反转特性。根据实验结果估算了材料参数。对于100 nm厚的薄膜，在0.8μm以下的线中观察到π壁的产生。对于0.6μ m宽的金属丝，由于畴壁成核的作用，反磁化强度随膜厚的增加而减小。4.<1-X>采用分子束外延技术在SrF_2衬底上生长了MnTe（反铁磁）/Ge_ Mn_xTe（铁磁）半导体耦合薄膜。在5 K下的磁滞回线中观察到50 Oe的回线位移。

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.