Mesoscopic studies on photo- induced magnetic effects in magnetic semiconductors

稀磁半导体（DMS）是自旋电子学的关键材料。然而，它们在微观意义上的磁性结构对应用具有重要意义，迄今为止还很少进行研究。在这里，我们直接观察了（Ga）的磁畴结构。Mn)为典型的III-V型半导体DMS薄膜，厚度分别为t=1.0和0.2μm。对于t=0.2μm的薄膜，我们进一步研究了光辐照对其磁性能的影响。采用MBE技术在25℃下生长具有平面内磁化特性的Mn) As薄膜。当t=1.0μm和t=0.2μm时，Mn含量分别为4.7%和5.3%。SSM测量在3K到100K的低温范围内完成。仪器检测垂直于样品表面的磁场Bz。从SSM观测中，我们发现了t= 1.0μm薄膜的异常圆畴。结果表明，在垂直方向上存在多个区域，边界较预期值弱。对于t=0.2μm薄膜。相比之下，我们观察到的是普通的条纹状畴。泄漏场达到300μT，与计算值接近。这告诉我们，t=0.2μm的薄膜是由垂直于薄膜表面的单一畴组成的。接下来，我们研究了t=0.2μm薄膜上的光致效应。结果发现，辐照后的Bz值约为辐照前的1.2倍。增强后的文件返回到原始文件。但反应相当缓慢。在3K时，确实需要大约50分钟才能达到最大值。反应速率随温度升高而降低。此外，我们证实了速率与光的强度成正比。在本实验中，我们首次观察到（Ga, Mn） As的磁性可以通过0.02mW/cm2的相对较弱的激光束增强。少

Diluted magnetic semiconductors (DMS) are key materials for spin electronics. However, their magnetic structures in a microscopic sense, which are important for applications, have been scarcely studied, so far. Here, we performed direct observations of magnetic domain structures in (Ga. Mn) As thin films, which is a typical DMS based on III-V semiconductors, with a thickness of t=1.0 and 0.2μm, by using a scanning SQUID microscope (SSM). For the t=0.2μm film, furthermore, we investigated the photo-irradiation effects on magnetic properties.(Ga. Mn) As thin films with in-plane magnetization were grown by the MBE technique at 25C. The Mn contents were 4.7% and 5.3% for t=1.0μm and t=0.2μm, films, respectively. SSM measurements were done at low temperatures ranging from 3K to 100K. The instrument senses the magnetic field perpendicular to the sample surface, Bz.From the SSM observations, we found anomalous circular domains for the t= 1.0μm film. The leakage field generated from the domain … More boundaries is weaker than the expectation, implying that multiple domains exist along the perpendicular direction. For the t=0.2μm film. In contrast, we observed ordinary stripe-shaped domains. The leakage field reached to 300μT, which is close to the calculated value. This tells us that the t=0.2μm film is composed of a single domain perpendicular to the film surface.Next, we have examined photo-induced effects on the t=0.2μm film. As a result, it was found that the Bz value under irradiation is approximately 1.2 times larger than the that before irradiation. The enhanced filed returned to the original one. But the reaction is substantially slow. At 3K, indeed, it took about 50min to reach to maximum. The reaction rate is decreased with increasing temperature. In addition, we confirmed that the rate is proportional to the intensity of light. In the present experiment, we observed, at the first time, that magnetism of (Ga, Mn) As can be enhanced by a relatively weak laser beam of 0.02mW/cm2. Less