In situ high-energy X-ray studies of magnetic-field-induced phase transition in a ferromagnetic shape memory Ni-Co-Mn-In alloy

The magnetic-field-induced phase transition behavior in a Ni₄₅Co₅Mn_36.6In_13.4 alloy, with and without an imposed stress, at various temperatures has been studied in situ by high-energy synchrotron X-ray diffraction. The crystallographic structure and microstructural characteristics in response to multiple external parameters (stress, temperature and magnetic fields) are traced, enabling the reversible and irreversible magnetic-field-induced transformations to be understood. The transformation kinetics as a function of temperature and magnetic field is determined by monitoring the changes of the specified diffraction peaks, which may be accurately described by the Clausius-Clapeyron relation. The X-ray absorption topographic measurements give direct evidence that inhomogeneous deformation occurred during magnetic-field-induced transformation in the polycrystalline materials. These investigations provide the fundamental structural information and functional characteristics that is crucial for the potential applications of this sort of new functional material. © 2007 Acta Materialia Inc.