Synthesis, Structure and Properties of III-V Ferromagnetic Semiconductor Thin Films

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Technical: The development of ferromagnetic, group III-V semiconductors has provided the potential for a class of multifunctional materials that exhibit magnetic, magneto-optical, and semiconducting properties. These materials offer the potential for manipulating both spin and charge. Their utilization, however, has been impeded due to their low transition (Curie) temperatures. Recently there have been reports of ferromagnetic semiconductors with Curie temperatures in excess of 300 K. There is growing evidence that disorder plays an essential role in stabilizing ferromagnetism in certain ferromagnetic semiconductors. The question arises as to the detailed mechanism for stabilizing the high temperature ferromagnetic phase and the nature of the magnetic species. In this project, narrow bandgap indium based III-V ferromagnetic semiconductor thin films will be developed, including InMnAs and InMnSb and their solid solutions. Of specific interest is what role transition metal atomic clusters play in stabilizing high temperature ferromagnetism in these semiconductors and the nature of the short range order. Furthermore the role of free carrier concentration on the ferromagnetic phase stability will be examined. During the project, epitaxial thin alloy films will be synthesized by metalorganic vapor phase epitaxy (MOVPE). Semiconductor alloys with different manganese concentrations will be prepared to determine the role disorder plays in stabilizing ferromagnetism. Recent models based on spinodal decomposition forming ferromagnetic clusters will be tested. Experimental characterization techniques to be used include temperature and field dependent magnetization measurements, Hall effect, and magnetoresistance. The magneto-optical Kerr effect (MOKE) and its spectral dependence over the mid infrared to visible region will be used to determine the nature and magnitude of the exchange interaction in the alloys. X-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD) at the Advanced Photon Source will be used to determine the magnetic properties of the elements comprising the alloys. Extended x-ray fine structure analysis (EXAFS), analytical electron microscopy, and an electrode atom probe with atomic scale resolution will be used to determine cluster size and distribution. Comparisons will be made between cluster sizes determined by structural and magnetic measurements.Non-technical: The project addresses basic research issues in a topical area of materials science with high technological relevance, and is expected to provide scientific understanding of ferromagnetic semiconductor materials with potential applications for spin based devices such as spin valves, magnetic random access memories, and quantum computation. The project provides training of graduate and undergraduate students in an interdisciplinary topic, consisting of semiconductor physics and magnetism. The project also includes educational outreach activities to local schools and collaboration with national laboratories, which provide enhanced learning opportunities to students.