Studies of Spin-Electronic Materials Using Synchrotron Radiation

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This proposal was received in response to the Spin Electronics for the 21st century Initiative, Program Solicitation NSF 02-036. The proposal focuses on x-ray studies of spin-electronic materials using synchrotron radiation. Systematic investigation of short-range-order structure, chemical valency, and local magnetic moment around constituent atoms in magnetic semiconductors will be carried out using state-of-the-art synchrotron radiation techniques including extended x-ray absorption fine structure (EXAFS), near-edge x-ray absorption fine structure (NEXAFS) and x-ray magnetic circular dichroism (XMCD). In addition, interface morphology, compositional intermixing and diffusion depth profile of magnetic ions in various heterostructures used in spin-injection devices will also be investigated by grazing incidence x-ray scattering (GIXS) and angular dependence of x-ray fluorescence (ADXRF) techniques. The nanostructure information obtained from these x-ray experiments is important for understanding the mechanisms responsible for the special electronic and magnetic properties of innovative spin-electronic materials for device applications. The materials to be studied include digital alloys and random alloys of III-V magnetic semiconductors, some have already been found with a Curie temperature above the room temperature. Other magnetic compound semiconductors such as II-VI, II-IV-V2, and II-VI2 systems with room-temperature ferromagnetism will also be investigated. These experimental approaches are based on this research team's extensive experience in the past decade of using x-ray scattering, fluorescence, and absorption techniques for nondestructive characterization of III-V magnetic alloy semiconductors and heterostructures. This group makes use of both soft and hard x-rays with both linear and circular polarization for materials research. Not many other x-ray research teams are doing experiments in both wavelength regimes with both types of polarization. The nanostructure information obtained in these experiments will be used as a feedback to crystal/epilayer growers for nondestructive evaluation of the materials, and from which to select more appropriate conditions for improving the material characteristics to meet device requirements. For the upcoming fiscal years 2002-2004, this research program will emphasize on the following areas: (i) local structures around magnetic ions in magnetic alloy semiconductors and magnetic digital alloys, and (ii) interface morphology, compositional intermixing and diffusion depth profile of magnetic ions in heterostructures of magnetic semiconductors and metals/alloys as well as their relation with spin-injection efficiency. The proposed research is expected to make significant contributions to both fundamental understanding of layered magnetic semiconductors and applications of the new magnetic materials in the exciting field of spin-electronics.