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Charles D. Graham, Jr. Professor Emeritus 222 LRSM 215.898.8509 cgraham@lrsm.upenn.edu |
Ph.D., Physical and Theoretical Metallurgy, University of Birmingham, 1954.
B.Met.E., Metallurgical Engineering, Cornell University, 1952.
Research Interests
Magnetic materials, including permanent magnet materials. Soft magnetic materials and amorphous alloys, and materials for magnetic recording.
Current Research Projects
Current work includes the investigation of asymmetric hysteresis loops in amorphous ferromagnetic alloys annealed in small but non-zero magnetic fields. These materials can produce a unique magnetic "signature" when used as markers in anti-shoplifting systems, and so greatly reduce the incidence of false alarms.
The work has been done in active collaboration with a major US producer of anti-theft systems. The behavior results from a difference in the physical location of nucleation sites of magnetic domains for opposite directions of magnetization reversal. There is an accompanying shift in the hysteresis loop along the field axis, resulting from the formation of a high coercive surface layer during the anneal.
Other recent projects include the mechanism of formation of crystallographic texture in Nd2Fe14B magnets made by a rapid solidification technique. The texture develops by hot compression in a normally-brittle material, and only when the grain size is extremely small. The proposed mechanism requires the presence of a liquid phase at the grain boundaries at the hot-working temperature, and involves the preferential transport of matter from random to oriented grains by liquid-phase diffusion.
In addition, cooperative research with industry is in progress on the behavior of magnetic powders in liquids under high fields, and on the influence of mechanical stress on the magnetic properties of high-saturation alloys. A more fundamental program is on the magnetic structure of amorphous alloys under high magnetic fields.
Selected Publications
"Measurements in Magnetic Materials," article in Concise Encyclopedia of Magnetic & Superconducting Materials, edited by J. Evetts, Pergamon Press (1992)
"Magnetic Materials," article in Encyclopedia of Applied Physics, VCH Publ., NY (1994).
"Magnetic Materials," chapter in Microstructure and Properties of Materials, edited by J. C. M. Li, World Scientific Publ. (1996)
Editor for English: S. Chikazumi, Physics of Ferromagnetism. Oxford Univ. Press (1997)
"High Temperature Magnetostriction Behavior of Fe-Co
Alloy", with B. Lorenz. to be published, J. Mag. Soc. Japan,
(1999)
