Pathways of structural and magnetic transition in ferromagnetic shape-memory alloys

A fundamental question in the study of ferromagnetic shape-memory alloys is, what is the nature of the magneto-elastic coupling in these alloys and to what extent does it drive 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 completely enslaved to and follows the martensitic structural transformation in these alloys, using Ni--Mn--Ga and Fe--Pd systems. This is determined by developing a new high-speed electronic method to study temperature-dependent domain dynamics, called ``magnetic transition spectra.'' The sequence of structural and magnetic transitions was found to be as follows: Cooling: structural transition followed by micromagnetic reconfiguration; Heating: micromagnetic reconfiguration followed by structural transition.