Structural and magnetic properties of Ni2CoSi: First-principles calculation and experimental realization

BCC Heusler phase Ni2CoSi has been predicted to be a promising candidate to realize magnetic field induced martensitic transformation. We tried to prepare Ni2CoSi single phase using different methods. Single phase Ni2CoSi cannot be synthesized by arc-melting and annealing. Then we used mechanical alloying method to synthesize Ni2CoSi. But a FCC phase rather than BCC was obtained after ball-milling. The lattice constant of FCC Ni2CoSi is 3.52 Å and the Curie temperature is around 900 K. The saturation magnetization at 5 K is 2.44μB/f.u. This FCC phase is stable and no transition is observed when heating to 1173 K. The electronic structure and phase stability of the FCC and BCC Heusler phase have been investigated by first-principles calculations. The FCC Ni2CoSi has lower total energy compared with BCC, agreeing with the experimental observation. But the calculated total moment is much smaller than the Ms at 5 K. This difference is related to the atomic disorder and was discussed by KKR-CPA calculation.