Materials Science & Engineering
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Item Combinatorial Investigation of Magnetostrictive Materials(2007-08-24) Hattrick-Simpers, Jason Ryan; Takeuchi, Ichiro; Wuttig, Manfred; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Combinatorial materials synthesis is a research methodology, which allows one to study a large number of compositionally varying samples simultaneously. We apply this technique in the search for novel multifunctional materials. The work presented here will discuss the combinatorial investigation of novel magnetostrictive materials. In particular, binary Fe-Ga and the ternary Fe-Ga-Al, Fe-Ga-Pd systems are studied. Magnetron co-sputtered composition spread samples of the alloys have been fabricated to study composition dependent trends in magnetostriction. Magnetostriction measurements on all systems studied here have been carried out by optically measuring the deflection of micro-machined cantilever arrays. Measurements of the magnetostriction on binary Fe-Ga thin-films show similar compositional trends as had been reported in bulk systems. The maximum value of magnetostriction observed is 220 ppm, which is comparable to bulk values. A previously unreported minor maximum in magnetostriction as a function of composition has been found for Ga contents of about 4 at%. It is believed that the origin of this minor maximum is related to a peak in the magnetic moment of Fe atoms in Fe-Ga alloys at this composition. We have mapped the Fe-Ga-Pd and Fe-Ga-Al ternary systems. Large regions of the phase diagrams have been mapped out in a single experiment, and the observed magnetostrictive dependence on Ga content matches trends seen in bulk. It was found that the trend of magnetostriction deviated from that of bulk with the inclusion of as little as 1 at% Pd. The addition of up to 10 at % Al to Fe70Ga30 was possible without severe degradation of its magnetostriction.Item Elasticity in Ferromagnetic Shape Memory Alloys(2004-11-23) Dai, Liyang; Wuttig, Manfred; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ferromagnetic shape memory alloys (FSMAs) are a new class of active materials, which combine the properties of ferromagnetism with those of a diffusionless, reversible martensitic transformation. These materials are technologically interesting due to the possibility of inducing large shape changes with an external applied magnetic field; either inducing the austenite/ martensite transformation or rearranging the martensitic variant structure with an applied field will induce a reversible shape change. The dependence of a solid's elastic properties on temperature in the vicinity of a structural transformation provides insight into the nature of the transition. Therefore, the elasticity of Ni2MnGa and Fe3Pd were studied. The temperature dependence of the elastic constants of the austenitic Ni0.50Mn0.284Ga0.216 and Ni0.49Mn0.234Ga0.276 were studied by an ultrasonic continuous wave method. Anomalous behavior in austenite was observed, which indicates a premartensitic transition. The temperature dependence of the elastic constants in martensitic Ni0.50Mn0.284Ga0.216 indicates a structural phase change from the tetragonal to a second phase at lower temperature. Modeling this phase change as a reentrance transition reproduces the major aspects of the temperature dependence of the shear elastic constant, (C11-C12)/2. The elasticity as a function of temperature and magnetic field of Fe3Pd was studied as well. An abrupt change of the elastic constants at around 45OC indicates a possible premartensitic transformation. The magnetic field dependence of elastic constants also indicates a probably magnetic field induced transition.