Strain-controlled chiral magnons and spin-dependent Seebeck effect in tetragonal <i>β</i> -MnO ₂ altermagnet: a DFT study

In this work, We present a comprehensive density functional theory based on first-principle calculation of chiral magnons in tetragonal<i>β</i>-MnO₂, a collinear compensated altermagnet. Our calculations confirm the thermal and dynamical stabilities of the tetragonal lattice and reveal an antiferromagnetic (AFM) ground state with momentum-dependent spin splitting, characteristic of altermagnetic behavior. Heisenberg exchange parameters derived from DFT+Wannier analysis indicate dominant nearest-neighbor AFM interactions, enabling non-degenerate magnon modes. Spin-wave magnon spectra calculated via linear spin-wave theory demonstrate clear chiral magnon behavior, manifested as nonreciprocal dispersion and chirality-dependent band splitting, arising from exchange anisotropy interactions permitted by the crystal symmetry. Furthermore, the influence of strain on magnon excitations was systematically examined, revealing that compressive strain enhances while tensile strain suppresses the spin-splitting in magnon spectra, highlighting the tunability of magnonic properties through lattice-strain engineering. Additionally, we explored the orientational spin-dependent transport features of altermagnet<i>β</i>-MnO₂, such as spin-dependent Seebeck coefficient as a function of chemical potential at temperature using Boltzmann transport technique. These findings highlight<i>β</i>-MnO₂as a promising platform for spintronic and magnonic applications, offering field-free, unidirectional spin transport and tunable chiral excitations.