Phonon, Electron, and Magnon Excitations in Antiferromagnetic L1$_{0}$-type MnPt

Abstract

Antiferromagnetic L1$_{0}$-type MnPt is a material with relatively simple crystal and magnetic structure, recently attracting interest due to its high N{\'{e}}el temperature and wide usage as a pinning layer in magnetic devices. While it is experimentally well characterized, the theoretical understanding is much less developed, in part due to the challenging accuracy requirements dictated by the small underlying energy scales that govern magnetic ordering in antiferromagnetic metals. In this work, we use density functional theory, the Korringa-Kohn-Rostoker formalism, and a Heisenberg model to establish a comprehensive theoretical description of antiferromagnetic L1$_{0}$-type MnPt, along with accuracy limits, by thoroughly comparing to available literature data. Our simulations show that the contribution of the magnetic dipole interaction to the magnetocrystalline anisotropy energy of $K_{1}$=1.07$\times 10^{6}$\,J/m$^3$ is comparable in magnitude to the spin-orbit contribution. Using our result for the magnetic susceptibility of $5.25\times10^{-4}$, a lowest magnon frequency of about 2.02\,THz is predicted, confirming THz spin dynamics in this material. From our data for electron, phonon, and magnon dispersion we compute the individual contributions to the total heat capacity and show that the dominant term at or above 2\,K arises from phonons. From the Landau-Lifshitz-Gilbert equation, we compute a N\'{e}el temperature of 990--1070 K. Finally, we quantify the magnitude of the magneto-optical Kerr effect generated by applying an external magnetic field. Our results provide insight into the underlying physics, which is critical for a deep understanding of fundamental limits of the time scale of spin dynamics, stability of the magnetic ordering, and the possibility of magneto-optical detection of collective spin motion.