Magnetic field dependence of electrical resistivity and thermopower in Ni₅₀Mn₃₇Sn₁₃ ribbons

We report magnetization, magnetoresistance (MR) and magnetothermopower (MTEP) of melt spun Ni₅₀Mn₃₇Sn₁₃ ribbons which exhibit an austentite to martensite phase transition at a temperature (T_M) ≈ 294 K. Upon cooling from 400 K, dc-resistivity and thermopower show abrupt changes at T_M, indicating a change in the electronic density of states. The thermopower is negative from 400 K down to 10 K. Application of a magnetic field of μ₀H = 5 T decreases T_M by 5 K and induces large negative MR (-23%) but positive MTEP (9%) near T_M. While the MR is appreciable from T_M down to 10 K, MTEP is significant only below 60 K (MR = -2.5% and MTEP = +300% at 10 K). The magnetic field dependence of resistivity and thermopower show either reversible or irreversible behavior near T_M, depending on whether the sample is zero-field cooled or field-cooled, which indicates that the electronic band structure near T_M is magnetic history dependent.