The electronic structures of Ni 3 Al, Ni 3 Ga, Ni 3 In, and NiGa are studied by x-ray absorption near-edge spectra ͑XANES͒ at the Ni and Ga K edges. The XANES spectra are compared with those calculated with theory. The experimental XANES features for these compounds reflect the Ni-and Ga-p unoccupied density of states. The calculated magnetic moments for Ni 3 Al, Ni 3 Ga, and Ni 3 In are between 0.7-0.8 B /cell. The number of 3d holes per Ni atom is calculated for Ni 3 Al, Ni 3 Ga, and Ni 3 In. These numbers show correlation with heats of formation of the bulk compounds.

To understand the structural stability and magnetism in the intermetallic compound Ni 3 In, we have performed total energy and electronic structure calculations for Ni 3 In as well as Ni 3 Al in the cubic L1 2 , tetragonal D0 22 , and hexagonal D0 19 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 Ni 3 Al and other related intermetallics, Ni 3 In in the nonmagnetic state is predicted to energetically favor the D0 22 structure rather than the L1 2 structure. However, the L1 2 and D0 19 structures are found to be magnetically unstable while the D0 22 structure is not. Ferromagnetism would make the L1 2 structure slightly lower in energy than the D0 22 structure by merely 7 meV/f.u. Therefore, the present theoretical work suggests that Ni 3 In 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 Ni 3 Al and other related intermetallics, there would be a pressure-induced structural phase transition from the L1 2 to D0 22 in Ni 3 In 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.

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