Effect of oxygen on the magnetic coupling of a Mn thin film on Fe(0 0 1) substrate

The effect of oxidation on the Mn–Fe magnetic coupling is investigated through ab initio density-functional calculations on a Mn monolayer deposited on Fe(0 0 1) to which a top layer of O is added. The clean Mn surface is found to be in an in-plane antiferromagnetic order with moments of 3.98μB and −4.39μB on the two inequivalent atoms, the subsurface Fe moments being smaller than in the bulk case. The addition of oxygen changes the coupling to interlayer antiferromagnetic between Mn and Fe. The Mn atoms still bear large magnetic moments but slightly lower than in the absence of O. The Fe moments on the interface are slightly enhanced and the O atoms are also polarized with moments of 0.33μB oriented antiparallel to the Mn ones in the ideal structure. Structural relaxation in the clean surface case yields a small buckling on the Mn overlayer as result of different couplings between Mn moments and Fe substrate ones. The Mn–O bond length is found to shrink in the oxidized case from its ideal bcc value as a result of the strong bonding between Mn and O. However, the ground state magnetic configuration does not change with the relaxation.