A fundamental question in the study of ferromagnetic shap ememory alloys is the nature of magnetoelastic coupling and the extent it drives the structural transformation. This question also holds the key to developing new and optimized alloys that combine high strains at low switching field. In the present study it is shown that the reconfiguration of the micromagnetic structure is enslaved to and follows the martensitic transformation in these alloys using the NiMnGa and FePd alloy systems. This is determined by developing a new, high speed electronic method to study the temperature dependence of domain dynamics, called magnetic transition spectra. The sequence of magnetic and structural transition was found to be as follows. For cooling, structural transition followed by magnetic transition and for heating, magnetic transition followed by structural transition.

20 pages including 6 figures. Physical Review B, in review, portions of it appear in MRS 2003 Proceedings volume 785