Temperature dependence of thermoelectric power and thermal conductivity in ferromagnetic shape memory alloy Ni_(50)Mn_(34)In_(16) in magnetic fields

摘要

We report a study of the temperature dependence of thermoelectric power S and thermal conductivity k in the ferromagnetic shape memory alloy Ni_(50)Mn_(34)In_(16) in presence of zero and 20 kOe magnetic field. A peak is observed in both S and k just below the paramagnetic to ferromagnetic transition temperature (T_C) of this alloy. Further down the temperature another sharp change is observed both in S and k, and this latter change is associated with the austenite to martensite phase transition in this alloy. The low temperature peak (below ～50 K), which is usually observed in the temperature dependence of S and k in metallic systems, is absent in the present alloy system. The measured thermal transport properties of Ni_(50)Mn_(34)In_(16) are qualitatively different from those reported earlier for the well known magnetic shape memory alloy system Ni-Mn-Ga. We interpret the measured thermal transport properties using the changes in the electronic structure near the Fermi level. Apart from electronic structure, the scattering of conduction electrons and phonons by the twin boundaries introduced into the system during the martensitic transition also plays an important role in the temperature dependence of S and k.