First principles investigations of the magnetic properties and martensitic transformation in Mn2NiB Heusler alloy

The presented results of first principles calculations show that the tetragonal deformation of Mn2NiB with inverse Heusler structure (Hg2CuTi) leads to a decrease in the total energy of the system. Two minima in the dependence of the total energy of the compound on the c/a ratio are found for c/a = 0.94 and c/a = 1.33. The results indicate that the c/a ratio of 1.33 yields the smallest energy at T = 0 K. The total energy difference between the states of Mn2NiB at c/a = 1.33 and c/a = 1.0 is estimated to be of about 345 K. The Mn2NiB transition from cubic to tetragonal structure can help to avoid a singularity at the Fermi level in the density of states of the parent compound with the cubic Hg2TiCu structure. Martensitic (tetragonal) and austenitic (cubic) phase of Mn2NiB are found to be ferrimagnetic with antiparallel aligned Mn spin moments. The contributions of 3 d states from Ni(C)-eg, Mn(A)-eg and Mn(B)-t2g to the minority peak near the Fermi level are discussed. These states in DOS for minority spins is shifted towards higher energy with the tetragonal distortion c/a > 1.0. Upon the martensitic transition, the intensities of peaks corresponding to the DOS change, taking mutually reversed values.