First-principles molecular-dynamics study on the magnetic structure of Mn3Pt

Abstract

A first-principles molecular-dynamics (MD) approach to the magnetic structure of itinerant magnets is proposed and applied to the magnetic structure of Mn3Pt, which is a three-dimensional frustrated magnet with an octahedral configuration of Mn local magnetic moments and exhibits two ordered phases at temperatures below the Neel temperature. The theory is formulated by incorporating the first-principles tight-binding linear muffin-tin orbital Hamiltonian into the MD approach for itinerant magnets on the basis of the functional integral method and the isothermal MD technique, and determines automatically the magnetic structures of itinerant magnets at finite temperatures. Numerical results at 25 K for a 3×3×3 fcc unit cell reveal a triangular-type noncollinear magnetic structure, which is consistent with the experimentally-proposed magnetic structure of the low-temperature-ordered phase (D-phase). With increasing temperature in the D-phase region, the amplitude and the thermal average of Mn local moments were found to decrease gradually. The stability of the experimentally-suggested magnetic structure of the higher-temperature-ordered phase (F-phase) in Mn3Pt is discussed on the basis of the nonmagnetic ground-state density of states, which shows a sharp sub-peak consisting of the Eg states of Mn at the Fermi energy.