First-principles molecular spin dynamics study on the magnetic structure of Mn-based alloys with Cu3Au-type crystal structure

The magnetic and electronic structures of Mn3Pt and Mn3Rh, which are three-dimensional frustrated itinerant magnets with a Cu3Au-type crystal structure, have been investigated by means of the first-principles Molecular Spin Dynamics (MSD) method. The theory is based on the first-principles tight-binding linear muffin-tin orbital Hamiltonian combined with the functional integral method and the isothermal MSD technique, and allows us to determine automatically the magnetic structures of itinerant magnets at finite temperatures. The MSD calculations using a self-consistent site-dependent effective medium show that below the Néel temperature Mn3Pt with fixed crystal structure (Cu3Au structure) and volume exhibits a second-order transition from a triangular structure to another noncollinear phase with increasing temperature. Mn3Rh, on the other hand, shows no sign of a phase transition up to the Néel temperature. We found that the Mn-Eg DOS peak, which is responsible for the ferromagnetic couplings among the second nearest-neighbor Mn local moments, develops at the Fermi energy (EFEF) around 350 K for Mn3Pt, while the peak development for Mn3Rh occurs with increasing temperature slightly above EFEF.