Nickel clusters: The influence of adsorbates on magnetic moments

Magnetic moments have been measured for bare, isolated nickel clusters Ni(n) and their association complexes with carbon monoxide, oxygen, and hydrogen using a molecular beam deflection method. The moments measured for bare Ni(n) are in general agreement with those previously reported by Apsel [Phys. Rev. Lett. 76, 1441 (1996)], lying slightly lower overall. It is found that adsorbed carbon monoxide and hydrogen decrease magnetic moments of Ni(n). The reduction in moments can be substantial for smaller clusters: the moment of Ni(8) is decreased by approximately 6 bohr magnetons by a single absorbed CO molecule. In general, the adsorbate-induced changes in magnetic moments diminish with increasing cluster size. The present results are in qualitative accord with previous measurements of the magnetization quenching effects of CO and H on nickel nanoparticles and thin nickel films. Atomic oxygen decreases cluster moments of some nickel clusters and increases those of others, an effect attributed to adsorbate-induced reconstruction. The experimental results are compared to detailed electronic structure calculations of nickel cluster-adsorbate complexes and to the predictions of the semiempirical bond order-rigid band model of Fourier and Salahub [Surf. Sci. 238, 330 (1990)]. (C) 2002 American Institute of Physics.