CAREER: Seeking Half-Metallic Alloys

Louisiana State University, Baton Rouge LA

Investigators

Abstract

Technical This CAREER project addresses fundamental materials science research on the synthesis, processing and characterization of half-metallic alloys. Through theoretical predictions, some full-Heusler alloys have been predicted to be half-metallic. Two such systems are Co2MnSi and Co2MnGe, neither of which exhibits half-metallic character, which may be related to the presence of antisite disorder, a condition, e.g., where Co atoms are substituted in the Mn sublattice in the full-Heusler L21 structure. Co antisite occupancy results in unwanted states appearing in the minority band gap, and therefore in the consequential reduction of the spin polarization, precluding the use of Heusler alloys in spintronic devices. A fundamental goal of this project is to reduce or avoid the adverse effects of Co antisite disorder in highly spin polarized full-Heusler alloy systems. In the near-stoichiometric Heusler alloys Co2MnZ, the effects of pulsed laser deposition growth parameters on the antisite disorder and spin-polarization will be determined. In particular, the effects of an applied magnetic field at the substrate during the growth of thin films will be explored. It is suggested that this will increase the magnetic ordering of the system and may directly reduce the degree of Co antisite occupancy. Non-Technical This project is expected to have a broader impact on science and education. As an integral part of research and education, a unique undergraduate course is proposed which essentially comprises an introduction to "real" research methods. It is a two-semester course that is focused on magnetism and magnetic materials. In the first semester, the fundamentals of magnetism are covered in order to provide a theoretical background. The second semester focuses on the principle measurement techniques and is lab-intensive. A sequence of six labs is designed to mimic a real research project from conception to communicating the results in both verbal and written forms. They start with bulk fabrication (making pulsed laser deposition targets), bulk characterization, thin film growth, thin film characterization, data analysis, and writing and presenting results. Scientific results that are obtained may open vistas for new research. For instance, new spin-polarized nonstoichiometric variants of Heusler alloys, if they were discovered, would immediately be the subject of many new studies. The discovery of an industrially functional highly spin-polarized material, or an ideal half-metal, would greatly influence the design of existing magnetoelectronic devices and, more importantly, ignite the pursuit of new ones. The project could have a profound impact on society. A real half-metal could be exploited in devices that range from sensors to magnetic random access memory. These devices could be employed to improve many aspects of our lives, from medical systems to computers. Additionally, a new doctoral program in applied physics has recently been approved in the Department of Physics at Southern Illinois University, admitting students in 2005. Over the five-year duration, this project is expected to fund nine graduate students who will be among the first to receive Ph. D. degrees in this department. This proposal will also fund about 8-10 undergraduate students, giving them the opportunity to experience many facets of magnetic materials research in a scientifically and socially diverse environment. The educational activities are designed to actively recruit students, including those from underrepresented groups, into the field of magnetic materials research.