Surface magnetism of oxygen and hydrogen adsorption on Ni(111)

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Abstract
The changes of surface magnetization and of surface anisotropies of Ni(111) surfaces during adsorption of oxygen and hydrogen were measured at room temperature using torsion oscillation magnetometry in situ in UHV (UTOM) of ultrathin epitaxial Ni(111) films on Re(0001). In the case of oxygen, a rapid chemisorption process is connected with an initial change in magnetic moment per O atom, Δμox=−4.5μNi (bulk Ni moment μNi), which is reduced to −3.8μNi in the saturated chemisorption state (θ= (1)/(3) ). This chemisorption is followed by a slow oxidation up to three layers of epitaxial NiO, connected with a change of the film moment Δm=−2.7mML (moment mML of bulk Ni monolayer). Surface anisotropy fields are reduced from (10±1) T (free surface) to (0±1) T both for chemisorbed and oxidized surfaces. For the case of hydrogen, saturation adsorption at room temperature (θ= (1)/(2) ) results in ΔμH=−1.6μNi and a reduction of the surface anisotropy field to (3±1) T.