First-principles study of electron, phonon, magnon dispersions and heat capacities of antiferromagnetic L₁₀-type MnPt

Electron, phonon, and magnon dispersions are important to understand magnetic phenomena such as anisotropic magnetoresistance or inelastic neutron scattering. First-principles density functional theory enables simulations of these three contributions. We investigate the energy dispersions and heat capacities of antiferromagnetic L₁₀-type MnPt, which is commonly utilized as a pinning layer to induce exchange bias in a ferromagnetic layer. The calculated energy dispersions lead to temperature-dependent heat capacities. The magnon dispersion from a Heisenberg model, including calculated exchange parameters and anisotropy energy, verifies the existence of a gap at the Gamma point. The T³ dependence of heat capacity at low temperature is originated from the phonon contribution, whereas the magnon contribution for heat capacity is absent at low temperature due to the magnon gap. At high temperature, the magnetic heat capacity from Monte Carlo calculations shows a peak, which is associated with the N\'eel temperature. The energy dispersion and heat capacity of antiferromagnetic L₁₀-type MnPt provide insight into studies of other properties such as temperature-dependent magneto-optics.