Intellectual merit: The development of ferromagnetic III-V semiconductors has provided the potential for a new 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. The PI has shown that InMnAs alloys prepared by metalorganic vapor phase epitaxy (MOVPE) exhibit a Curie temperature of 330 K. His recent research indicates that atomic clusters are responsible for the enhanced Curie temperature. The question arises as to the detailed mechanism for stabilizing the high temperature ferromagnetic phase and what is the nature of the magnetic species. In the proposed program In based III-V ferromagnetic semiconductor thin films will be studied including InMnAs, InMnSb, InMnP and their solid solutions. Of specific interest is what role do transition metal atomic clusters play in stabilizing high temperature ferromagnetism in these semiconductors and what is the nature of the short range order. The role of free carrier concentration on the ferromagnetic phase stability will also be examined. It is planned to determine whether or not other In based III-V compounds can be synthesized by MOVPE with Curie temperature in excess of 400 K as predicted by recent theory. In this project, epitaxial thin alloy films will be synthesized by metalorganic vapor phase epitaxy. Semiconductor alloys with different band gaps will be prepared to determine the role that band mixing, impurity ionization energy and degree of carrier localization play in stabilizing ferromagnetism. Experimental characterization techniques to be used include high resolution transmission electron microscopy, temperature and field dependent magnetization measurements, Hall effect and magnetoresistance. The magneto-optical Kerr effect (MOKE) and its spectral dependence over infra-red to visible region will be used to determine the nature and magnitude of the exchange interaction in the alloys. Extended x-ray fine structure analysis (EXAFS) and a local electrode atom probe with atomic scale resolution will be used to determine cluster size and distribution. 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. X-ray photo-electron electron microscopy (PEEM) at Argonne will be used in conjunction with temperature dependent magnetic force microscopy to determine magnetic domain structure and stability. Non-Technical. Broader impact: The project will involve the training of graduate and undergraduate students in the synthesis and property measurements on ferromagnetic semiconductors. Students will also be involved in synchrotron studies at Argonne. These materials have potential technological importance for new types of spin devices such as spin valves, magnetic random access memories and quantum computation devices.
