Ab initio studies of structural stability and magnetism in Ni₃In

To understand the structural stability and magnetism in the intermetallic compound Ni₃In, we have performed total energy and electronic structure calculations for Ni₃In as well as Ni₃Al in the cubic L1₂, tetragonal D0₂₂, and hexagonal D0₁₉ structures. The highly accurate full-potential linearized augmented-plane-wave method has been used. The calculations are based on first- principles density-functional theory with generalized gradient approximation. The theoretical equilibrium lattice constants and bulk moduli of both the compounds are in good agreement with available experiments. Surprisingly, unlike Ni₃Al and other related intermetallics, Ni₃In in the nonmagnetic state is predicted to energetically favor the D0₂₂ structure rather than the L1₂ structure. However, the L1₂ and D0₁₉ structures are found to be magnetically unstable while the D0₂₂ structure is not. Ferromagnetism would make the L1₂ structure slightly lower in energy than the D0₂₂ structure by merely 7 meV/f.u. Therefore, the present theoretical work suggests that Ni₃In at low temperatures is a weak ferromagnet and undergoes a structural and magnetic phase transformation as the temperature is raised to the room temperature. This picture would allow one to consistently interpret previous structural experiments and measured x-ray absorption spectra. Moreover, it is also predicted that unlike Ni₃Al and other related intermetallics, there would be a pressure-induced structural phase transition from the L1₂ to D0₂₂ in Ni₃In at low temperatures. It is hoped that these interesting findings would stimulate further experimental investigations such as temperature-dependent structural, specific-heat, and magnetization experiments on this nearly or weakly magnetic intermetallic compound.