Magnetism of an ultrathin Mn film on Co(100) and the effect of oxidation studied by x-ray magnetic circular dichroism - art. no. 214406

The electronic and magnetic structures of a Mn ultrathin film grown on a 3- ML (monolayer) Co film have been investigated during stepwise oxidation by means of O K-, Mn L-III,L-II-, and Co L-III,L-II-edge x-ray-absorption spec troscopy and Mn L-III,L-II-, and Co L-III,L-II-edge x-ray magnetic circular dichroism (XMCD). Without O-2, strong interaction between the Mn and Co 3d orbitals was suggested and Mn-Co ferromagnetic coupling was confirmed. We observed significant suppression of the d hole number and the spin and orbi tal moments of Co after Mn deposition compared to those before Mn depositio n. These findings imply that the Mn d electrons are transferred to the mino rity-spin levels of Co. At 0.5-L (Langmuir) O-2 exposure, the spin and orbi tal moments of Co do not change noticeably, while the Mn L-III,L-II-edge XM CD almost completely vanishes. After 5.5-L O-2 exposure, an antiparallel sp in alignment between Mn and Co was observed. The estimated orbital moments of Mn is reduced from 0.06 (before oxidation) to < 0.005<mu>(B) (after oxid ation). It is concluded that unoxidized Mn is in the d(5) + d(6) State whil e oxidized Mn is in the d(5) high-spin state. Such variance of the electron configuration of Mn can explain the unusual magnetic properties. Antiferro magnetic coupling between Co and oxidized Mn may originate from the d(5) hi gh-spin configuration of Mn rather than from the superexchange interaction between Mn and Co via the O atom.