Phase stability and physical property for off-stoichiometric Ni-Mn-Sb alloys including 4O phase

Large magnetic field-induced strains can only be found in modulated martensite for Ni-Mn-Sb alloys, but the theoretical research on this alloy which is generally concentrated in the austenite and non-modulated martensite (NM) ignores the modulated martensite. Therefore, in this paper, we systematically study the relationship between phase stability, physical property and composition in the full series Ni-Mn-Sb Heusler alloys (Ni _{24+ x}Mn _{12- x}Sb ₁₂, Ni _{24+ x}Mn ₁₂Sb _{12- x}, Ni _{24- x}Mn _{12+ x}Sb ₁₂, Ni ₂₄Mn _{12+ x}Sb _{12- x}) including four-layered orthorhombic modulated martensite (4O) by the first principles calculations. For phase stability, we determined that the critical components of 4O for Ni _{24+ x}Mn _{12- x}Sb ₁₂, Ni _{24+ x}Mn ₁₂Sb _{12- x} and Ni ₂₄Mn _{12+ x}Sb _{12- x} is × = 6, x = 6 and × = 4, respectively. There is no 4O phase within the concentration range considered for Ni _{24- x}Mn _{12+ x}Sb ₁₂. Moreover, the martensitic transformation sequences are also determined. As for physical properties, the transformation temperatures from austenite to 4O and NM phases are predicted respectively. Meanwhile, the ternary magnetic moment diagram of austenite, 4O and NM phases is constructed. The maximum value of total magnetic moment is distributed in the Ni-excess Sb-deficient system, while the minimum value of that is distributed in the Mn-excess Sb-deficient system. The origin of the above observations is explained by the competition between the Jahn-Teller effect in the electronic structure and the strength of the covalent bond. The results in this paper are expected to provide information for the composition design and performance optimization of Ni-Mn-Sb alloy.