Abstract
We report magnetization, magnetoresistance (MR) and magnetothermopower (MTEP) of melt spun Ni50Mn37Sn13 ribbons which exhibit an austentite to martensite phase transition at a temperature (TM) ≈ 294 K. Upon cooling from 400 K, dc-resistivity and thermopower show abrupt changes at TM, 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 TM by 5 K and induces large negative MR (-23%) but positive MTEP (9%) near TM. While the MR is appreciable from TM 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 TM, depending on whether the sample is zero-field cooled or field-cooled, which indicates that the electronic band structure near TM is magnetic history dependent.
Highlights
Magnetization of magnetic Heusler alloys, there are few combined studies of thermopower and electrical resistivity
Thermopower in ferromagnetic Ni2+xMn1−xGa is negative and shows a dip at the martensite and premartensite transition temperatures for x = 0.13-0.19.19,20 It was reported that density of states (DOS) changes at the austenite to martensite (A-M) transition in Ni-Mn-Ga alloys.[21]
A paramagnetic (PM) to ferromagnetic (FM) transition at TC(A) = 299 K followed by an abrupt decrease in magnetization at T = TM = 294 K due to the austenite to martensite (A-M) structural transition under μ0H = 0.1 T
Summary
In the non-magnetic shape memory alloy Ti50Ni50, the thermopower is positive in sign and shows an abrupt increase (decrease) during the A-M (reverse) phase transition.[18] On the other hand, thermopower in ferromagnetic Ni2+xMn1−xGa is negative and shows a dip at the martensite and premartensite transition temperatures for x = 0.13-0.19.19,20 It was reported that density of states (DOS) changes at the A-M transition in Ni-Mn-Ga alloys.[21] the negative thermopower in Ni50Mn34In1622 and Mn2NiGa23 shows an abrupt decrease in magnitude at the A-M transition during cooling, and the anomaly at TM is very weak in Ni50Mn36Sn14. The Ni50Mn50−xSnx alloys have been studied by different research groups because of the significance for the magnetocaloric effect[24] and magnetoresistance,[25] but simultaneous measurements of resistivity and thermopower and the impact of external magnetic field on these properties were not reported so far. We studied the influence of external magnetic field on the electrical resistivity and thermopower in Ni50Mn13Sn13 ribbons
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