Lattice dynamics and spin-phonon coupling in the noncollinear antiferromagnetic antiperovskite Mn3NiN

Antiferromagnetic antiperovskites, of the form Mn₃ B N (B = Ni, Cu, Zn, Sn, Ir, and Pt), have shown an outstanding behavior in which, giant negative thermal expansion and chiral magnetic structures are intertwined. As such, aiming to shed light on the magnetostructural behavior, related to the magnetic ordering and crystalline structure of this type of materials, we studied theoretically, based-on first-principles calculations, the lattice dynamics and spin-phonon coupling in the Manganese-based antiperovskite Mn₃NiN, as a prototype in the Mn₃ B N family. We found a strong spin-lattice coupling by means of the understanding of the phonon-dispersion curves obtained when including the chiral noncollinear magnetic structures. To do so, we highlight the importance of the exchange-correlation scheme selected and its influence on the structural, electronic, magnetic, and vibrational degrees of freedom. Finally, we found two unstable vibrational modes at the M- and R-points when the magnetic ordering is switched to ferromagnetic from the chiral Γ_4g and Γ_5g. These octahedral-associated modes with spin-phonon coupling parameters, λ, as large as 10.74 cm^-1 and -2.53 cm^-1 for the R₅^-, and M₂⁺ , respectively. The latter coupling is observed as a key signature of the strong spin-lattice interaction.