Defect Stability and Magnetic Property of Ni-Mn-Sn Alloys by First-Principles Calculations

Ni-Mn-Sn alloy is a new type of ferromagnetic shape memory alloy with great potential for the industrial application. Chemical composition has a great influence on the martensitic transformation and magnetic properties for the nonstoichiometric Ni2Mn1-xSn1-x alloys. A large number of the point defects will be generated during the composition tuning process. In this work, the effects of point defects including antisites, vacancies, and atomic exchanges on the phase stability, magnetic property and electronic structure of the Ni-Mn-Sn alloy were investigated by using the first-principles calculations. Generally, the phase stability, magnetic and elastic properties of alloys with different compositions can be studied efficiently and economically by means of the first-principles calculations. Moreover, the ground state energy, driving force of phase transformation, and atomic magnetic moments of the parent phase and the product phase, which cannot be directly obtained by experiments, can be alternatively investigated through the first-principles calculations. The formation energy of most of the point defects is negative, indicating that these defects can form and stay stably in the parent phase of the non-stoichiometric Ni-Mn-Sn alloy. In particular, the Mn-rich and Sn-deficient Ni-Mn-Sn alloy is commonly used composition design during previous experimental studies. Martensite transition can be controlled effectively by adjusting the Mn and Sn contents. A large number of Mn-Sn antisite defects with relatively lower formation energy would be generated in the parent phase of the Mn-rich and Sn-deficient Ni-Mn-Sn alloy. The formation of the Sn vacancy dramatically reduces the stability of the parent phase. This change will promote the martensitic transformation of the alloy. When the excess Mn atom occupies Sn site, the 30% decrease of the Mn-Mn distance leads the magnetic moment of the excess Mn antiparallel to that of the normal Mn. The smaller Ni-Mn distance causes a larger Ni moment. This study may provide a better understanding of the martensitic transition and physical properties for the Ni-Mn-Sn alloy.