IEEE Santa Clara Valley Section  

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IEEE Magnetics Society
Santa Clara Valley Chapter
Meeting Presentation Summary

Thursday, January 19, 2012

San Jose State University College of Engineering Building, Room 285/287
Seventh Street and San Fernando Steet, San Jose CA

Directions and Map

Cookies, Conversation & Pizza too at 7:00 P.M.
Presentation at 7:30 P.M.

Phase Evolution in the Fe3O4-Fe2TiO4 Pseudo-binary System
and its Implications for Remanent Magnetization in Martian Minerals.

Professor Michael E. McHenry
Carnegie Mellon University


Our NSF funded Materials World Network aims to determine the role of nanostructure on the temperature dependent remanent magnetic state of spinodally decomposed two phase mixtures in the Fe3O4-Fe2TiO4 pseudo-binary titanomagnetite system. The research investigates the role of these minerals on terrestrial and extraterrestrial magnetic field anomalies and uses magnetic measurements to probe decomposition kinetics. The titanomagnetites are important commonly occurring minerals on the moon and Mars. Since both lack an intense global magnetic field, magnetic mapping is even more powerful on these two bodies than on Earth where magnetic surveys are complicated by the presence of the main field, which makes measurements of crustal anomalies challenging. The global magnetic mapping and the study of the minerals of the crust and surface and their remanent state can give clues to the geomagnetic evolution of a planet. The pseudo-binary Fe3O4-Fe2TiO4 system is an interesting system for using magnetic measurements to probe the kinetics of phase transformations. This oxide system has a miscibility gap with spinodal decomposition. The two phases appearing in the decomposition are magnetite and an antiferromagnetic ulvospinel. Homogeneous metastable solid solutions can be non-magnetic at temperatures where decomposition kinetics can be monitored in reasonable experimental times. The magnetixzation of the magnetite formed by the decomposition reaction is a measure progress of the transformation. Time-dependent magnetization measurements will be described that monitor the kinetics of spinodal decomposition for compositions within the spinodes and nucleation and growth kinetics for compositions outside of the spinodes. We have developed synthesis routes for compounds in the pseudo-binary Fe3O4-Fe2TiO4 system that allow us to more accurately define the asymmetric miscibility gap in this system. The fine microstructure resulting from spinodal decomposition and exchange anisotropy mechanisms for coupling may explain a large slowly decaying remanent state for these minerals on Mars. Certain compounds are of further interest because they have magnetic transitions that are within the day to night temperature swing on Mars and can therefore be detected with miniaturized magnetic sensors.


Photo of AUTHOR Michael E. McHenry is Professor of Materials Science and Eng. (MSE), with an appointment in Physics at Carnegie Mellon. He graduated with a B.S. in Metallurgical Eng. and Materials Science from Case Western Reserve in 1980. From 1980 to 1983 he was employed as Process Engineer at the U.S. Steel Lorain Works. In 1988 he earned a Ph.D in Materials Science and Eng. from MIT. He was a Director's Funded Post-doctoral Fellow at Los Alamos Lab from 1988 to 1989. He has expertise in the area of nanocrystalline magnetic materials including soft magnetic nanocomposites, faceted ferrite nanoparticles and materials for power conversion, biomedical, energy and data storage applications. His research involves rapid solidification processing, plasma and solution synthesis of nanoparticles, magnetic field of processing materials, structural characterization by x-rays and electron microscopy and magnetic properties characterization as a function of field, temperature and frequency. He directed a Multidisciplinary University Research Initiative (MURI) on high temperature magnetic materials for aircraft power applications and currently leads an ARPA-E program in magnetic materials for power electronics. He has served as proceeding Editor, Publication Chair and a member of the Program Committee for the Magnetism and Magnetic Materials (MMM) and Intermag Conferences. He has published over 250 papers and owns two patents in the field. He has co-authored, with Marc DeGraef, the textbook “Structure of Materials”, Cambridge University Press, 2007.



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