By combining theoretical density functional theory (DFT) and experimental studies, structural and magnetic phase stabilities and electronic structural, elastic, and vibrational properties of the Laves-phase compound ${\mathrm{NbMn}}_2$ have been investigated for the C14, C15, and C36 crystal structures. At low temperatures C14 is the ground-state structure, with ferromagnetic and antiferromagnetic orderings being degenerate in energy. The degenerate spin configurations result in a rather large electronic density of states at Fermi energy for all magnetic cases, even for the spin-polarized DFT calculations. Based on the DFT-derived phonon dispersions and densities of states, temperature-dependent free energies were derived for the ferromagnetic and antiferromagnetic C14 phase, demonstrating that the spin-configuration degeneracy possibly exists up to finite temperatures. The heat of formation ${\mathrm{\Delta }}_{298}{H}^0=-45.05\pm 3.64\mathrm{kJ}{(\mathrm{mol}\mathrm{f}.\mathrm{u}.{\mathrm{NbMn}}_2)}^{-1}$ was extracted from drop isoperibolic calorimetry in a Ni bath. The DFT-derived enthalpy of formation of ${\mathrm{NbMn}}_2$ is in good agreement with the calorimetric measurements. Second-order elastic constants for ${\mathrm{NbMn}}_2$ as well as for related compounds were calculated.

• Received 13 December 2017
• Revised 21 February 2018

DOI:https://doi.org/10.1103/PhysRevB.97.125110