| Research Abstract |
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
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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
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