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Friday, March 23, 2018 at 1:00pm
"STRAIN-INDUCED FERROMAGNETISM IN INTERMETALLIC COMPOUNDS"
Abstract: It has been known for over forty years that B2-structured FeAl can undergo a paramagnetic to ferromagnetic transition upon cold working. Strain-induced ferromagnetism (SIF) in FeAl arises from the generation of APB tubes, where Fe atoms can have ≥3 like nearest neighbors. The resulting saturation magnetization, Ms, depends on both the Fe:Al ratio, the presence of substitional alloying elements and the degree of deformation. This presentation will outline a quantitative model that describes the effects of these parameters in terms of the local environment theory applied to the atoms in APB tubes. SIF in the L21-structured compound Fe2AlMn will also be outlined and explained by considering the site preferences of ternary atoms on the Fe and Al sublattices. The value of Ms depends on whether this compound is in the B2 or L21 state, and can show values up to 96 emu/g - by comparison pure nickel is 59 emu/g. TEM observations of APB tubes in lightly-strained single crystals of FeAl and Fe2AlMn will be presented, and the annealing out of APB tubes and the associated activation energy will be discussed. The effects of plastic strain on the magnetic properties of some strongly-ordered L12 intermetallics will also be briefly outlined. Finally, we will briefly discuss the role of APB tubes on the work-hardening of intermetallic compounds.