Role of magnetic and atomic ordering in the martensitic transformation of Ni-Mn-In from a first-principles study.

The composition-dependent lattice parameters, crystal structure, elastic properties, magnetic moment, and electronic structure of Ni2Mn1+xIn1-x (0⩽ x ⩽ 0.6) are studied by using first-principles calculations. It is shown that the martensitic phase transition (MPT) from cubic L21 to tetragonal L10 accompanies the MnMn-Mnin ferromagnetic (FM) to antiferromagnetic (AFM) transition, at around the critical composition x = 0.32, in agreement with the experimental measurement. The Mn-In atomic disorder leads to decreasing stability of the martensite relative to the austenite, which depresses the MPT. The shear elastic constant C' of the parent phase first decreases slightly with increasing x and then remains almost unchanged above x = 0.32, indicating C' alone cannot account for the increase of the MPT temperature with x. The total magnetic moments for the L21 phase are in good agreement with those determined by experiments, whereas for the L10 phase they are slightly larger than the experimental data due to the possible Mn-In atomic disorder in the sample. The calculated density of states demonstrate that the covalent bonding between the minority spin states of Ni and In plays an important role in both the magnetic and structural stability. [ABSTRACT FROM AUTHOR]