Abstract
The influence of both the Co addition and the internal stress on the atomic level magnetism is comparatively studied in Ni50Mn37Sn13 and Ni45Mn38Sn13Co4 alloys by magnetic measurements and 119Sn Mössbauer spectroscopy. The results show that the saturation magnetization and the hyperfine field follow the same temperature trend. The internal stress state is investigated by subjecting the samples to milling and annealing treatments, and tracking the singlet component revealed by 119Sn Mössbauer spectroscopy. Contrary to what was expected, in the Co-doped Ni-Mn-Sn sample the singlet component can be resolved between the milled and annealed states in both martensite and austenite phases. Therefore, the results demonstrate the feasibility of tracking the singlet component upon the structural recovery in Co-doped Ni-Mn-Sn alloys in a much wider range than in ternary alloys. In addition, it is concluded that the transferred dipolar field at Sn from the neighbor magnetic atoms depends very strongly on the stress field and on the microstructural order surrounding Sn atoms. The observed sensitivity of Sn Mössbauer probe atoms to slight microstructural distortions make 119Sn a powerful technique for the characterization of the stress present in Sn containing metamagnetic shape memory alloys.
Highlights
Ni-Mn-based Heusler alloys have been extensively studied during recent decades due to the multifunctional properties they exhibit such as giant magnetoresistance [1], magnetocaloric effect [2] and shape memory effect [3]
The results show that at 160 K, the singlet component is detectable in the Mössbauer spectra of the ternary alloy; at 64 K, the singlet fades out even in the milled state, where in principle, the AF coupling across the anti-phase boundaries (APBs) should still contribute with a singlet to the 119Sn Mössbauer spectra
The spectra were taken at 420 K and 300 K for the ternary and quaternary alloy, respectively
Summary
Ni-Mn-based Heusler alloys have been extensively studied during recent decades due to the multifunctional properties they exhibit such as giant magnetoresistance [1], magnetocaloric effect [2] and shape memory effect [3]. Their multifunctional properties are linked to the occurrence of the martensitic transformation (MT), which is a first order phase transition between a cubic austenite phase and a less-symmetric martensite one. This effect is especially notorious in Ni-Mn-In-Co alloys, in which an almost non-magnetic martensite phase is obtained showing enhanced magnetocaloric properties [8]. Ni-Mn-Sn alloys present a highly stable long-range atomic order structure against thermal treatments, becoming a good candidate for thermocycling involving applications [9]
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