Factors influencing the martensitic transformation in Ni 50 Mn 35 Sn 15 : an EXAFS study

Extended x-ray absorption fine-structure (EXAFS) measurements have been carried out on Ni₅₀Mn₃₅Sn₁₅ in the austenitic and martensitic phase. The temperatures associated with structural and magnetic phase transformations are obtained from magnetization measurements. The system orders ferromagnetically below 319 K while the structural phase transition occurs at TM ~ 200 K. EXAFS measurements have been carried out at Mn and Ni K-edges and changes associated with respect to the local structure of these absorbing atoms are compared. Significant changes in the nearest neighbour interactions are seen as the system transits to the low temperature martensitic phase. EXAFS provides evidence for local structural distortion even in the cubic phase that is not seen from the x-ray diffraction studies. The results obtained are understood in terms of changing hybridization between the constituent atoms that influence the electronic structure at the Fermi level, associated with the austenitic-to-martensitic transition.