Monday, 11 October 2004 - 1:25 PM

This presentation is part of : Active Materials

Magnetic Mosaics in Crystalline Tiles – A New Perspective on Ferromagnetic Shape Memory Alloys (Invited)

Matthew R. Sullivan1, Steven Pirotta, G. H. Wu2, Lourdes Salamanca-Riba3, and Harsh Deep Chopra1. (1) Thin Films and Nanosynthesis Laboratory, Materials Program, Mechanical and Aerospace Engineering Department, State University of New York at Buffalo, Buffalo, NY 14260, (2) State Key Laboratory for Magnetism, Institute of Physics , People’s Republic of China, Chinese Academy of Sciences, Beijing, 100080, China, (3) Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742

This work will discuss the temperature and field dependent evolution of the micromagnetic structure in ferromagnetic shape memory alloys (Ni-Mn-Ga, Fe-Pd, and Co-Ni-Ga). Results provide a new and simple perspective on these actuator materials – the micromagnetic structure of these alloys resembles a magnetic ‘mosaic’ contained within ‘tiles’ of the transformed martensite phase (twins). These results also answer the fundamental question, viz., what is the nature of the magneto-elastic coupling in these alloys and to what extent does it drives the structural transformation? It is shown that the temperature dependent reconfiguration of the micromagnetic structure is completely enslaved to and follows the martensitic transformation in these alloys. Direct micromagnetic evidence of field induced martensitic transformation is also shown. This field induced martensite transformation was found to be completely reversible. In analogy with the well known pseudo-elastic behavior in conventional shape memory alloys, this behavior is termed ‘magneto-pseudo-elastic’ or MPE effect. Remarkably, the MPE effect can be realized in fields (800 Oe) that are much lower than theoretically predicted values of several thousand oersteds. Finally, the concept of magnetic mosaics has been used to synthesize a novel class of materials with engineered magnetic anisotropies, and will be discussed. This work was supported by the DOE, Office of Basic Energy Science, Grant No. DE-FG02-01ER45906, and this support is gratefully acknowledged.

Back to Active Materials
Back to SES Abstracts

Back to The 41st Annual SES Technical Meeting