The influence of chemical disorder enhancement on the martensitic transformation of the Ni50Mn36Sn14 Heusler-type alloy

The effect of chemical disorder over the martensitic phase transformation of the Ni₅₀Mn₃₆Sn₁₄ Heusler-type alloy was systematically investigated by performing X-ray diffractometry (DRX), DC magnetization and ⁵⁷Fe-doping and ¹¹⁹Sn-Mössbauer spectroscopy measurements. DRX patterns are characteristics of a L2₁-type chemically disordered structure, where the presence of this disorder was first evaluated by analyzing the relative intensity of the (1 1 1) DRX reflection, which varies in the case of Fe-doped and practically disappears for the milled samples. In consequence, the magnetic properties of Fe-doped well-milled samples related to the martensitic phase transformation change substantially. 300 K ⁵⁷Fe-Mössbauer spectroscopy data suggest that the changes in the magnetic properties related to the martensitic transformation are intrinsically correlated to the ferromagnetic and paramagnetic fractions, which are respectively associated with Fe atoms replacing Mn- and Sn-sites. In the case of milled samples, the drastic reduction of alloy magnetization was explained by the increase of the number of Mn atoms in the shell regions, which have a reduced magnetic moment comparatively to those in the grain cores. The magnetization change and the temperature transition in the martensitic transformation are governed by the grain core. The initial magnetic properties and martensitic transformation can be recovered by a subsequent annealing on the milled sample.