Effect Of Co/Fe On The Structure And Magnetic Transformation Of Ni₅₀Mn₃₇Sn₁₃ Alloys

Abstract:Ni50Mn37Sn13、(Ni50Mn37Sn13)10-xCox and (Ni50Mn37Sn13)10-xFex (x=4,9) Heusler alloys were prepared by arc melting-melt spun annealing with high temperature. With moden measurements and the first principle calculation, we mainly foucs on the effect of Co/Fe on Ni50Mn37Sn13alloy in three aspects of the microstructure, phase transformation temperature and magnetic transformation.First of all, the experimental results indicate that all the ingots are dendritic crystal composited by martensite, austenite and some impurity phase; the ribbons consist of single austenite phase; the annealing-ribbons have the similar structure with the ingots. Besides, it is also shown that the composition super-cooling is increased by addition of Co/Fe, and the structure of these alloys has no change, which suggests that Co/Fe just occupy the Mn/Ni sites respectively.Moreover, the experiment results indicate that it has the significant change in the phase transition temperatures and the magnetic properties by addition of Co/Fe in Ni50Mn37Sn13alloy.①In (Ni50Mn37Sn13)10-xFex system, it results in the decreased martensitic phase transition temperature with little change of Curie temperature of austenite by addition of small amount of Fe. However, too much Fe makes the martensitic phase transition temperature disappear with an obvious increasing of Curie temperature of austenite. In addition, it can be seen that the refrigeration efficiency of the alloys is not reduced by addition of Fe because of the little change of the magnetic entropy change.②In (Ni50Mn37Sn13)10-xCox system, the martensitic phase transition temperature and Curie temperature of austenite are both increased by addition of a small amount of Co. And addition of excess Co lead to the martensitic phase transition temperature disappearing. Meanwhile, the magnetic entropy change is increased by addition of Co. These changes demonstrate that it is an effective way to improve the cooling efficiency of the alloy.Furthermore, the first principle calculation results show that Mn, Co/Fe atoms are the major contributor to the magnetism of the alloys. But Ni atoms almost have the negligible magnetic moment. In Ni50Mn37Sn13alloy it esists Ni-Mn ferromagnetic coupling and following the addition of Co/Fe, the Ni-Co and Fe/Co-Mn ferromagnetic coupling are strengthened. Besides, the metallicity is strengthened with the addition of Co/Fe according to the band structure analysis.