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

我们研究了载流子感生铁磁半导体Ge_(1-X)&Gt；Mn_xTe的磁化反转过程和磁性调控，得到了以下结果：1.测量了不同载流子浓度和不同Mn组分的Ge_&lt；1-X&Gt；Mn_xTe的磁阻。在假设钉扎场分布的情况下，通过模拟得到了旋转场的磁流变行为。样品中的钉扎场较大，表明在高磁场区域有较大的负磁阻。这表明阻碍磁化旋转的局域自旋的不均匀可能是磁极化子的形成。2.用电子束曝光技术制备了10~0.8μm的Ge&lt；1-X&Gt；MnxTe细丝。对于厚度为400 nm、Mn组分x=0.25的样品，当磁场沿纵向施加时，磁化强度在零场的倾斜随导线宽度的减小而减小。但纵向和横向的MR曲线无明显差异。综合第一节和第三节的结果，在所研究的样品中，局部区域的不均匀磁化反转似乎占主导地位。3.用微磁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，在宽度小于0.8πm的线材中观察到了μ壁的产生。采用分子束外延技术在SrF_2衬底上生长了nucleation.4.MnTe(antiferromagnetic)/Ge_&lt；1-X&gt；Mn_XTe(ferromagnetic)半导体耦合膜，对于0.6μm宽的线材，磁化反向场的幅度随膜厚的增加而减小。在5K的磁滞曲线上观察到50Oe的环移。

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.