Orbital polarization effects on the magnetic anisotropy and orbital magnetism of clusters, films, and surfaces: A comparative study within tight-binding theory Article uri icon

abstract

  • The effects of orbital polarizations on the magnetic properties of transition-metal nanostructures are investigated in the framework of a self-consistent tight-binding theory. Three different approximations to the intra-atomic two-center Coulomb interactions are considered: (i) full orbital dependence of the direct and exchange Coulomb interactions Um m′ and Jm m′ as given by atomic symmetry, (ii) orbital independent interactions U= Um m′ ̄ and J= Jm m′ ̄, and (iii) orbital polarization (OP) approximation of the form HOP =-(B 2) Σ i Li2, where Li refers to the orbital momentum operator at atom i and B to the Racah coefficient. Results are given for the local orbital magnetic moments Liδ along high-symmetry magnetization directions δ and for the corresponding magnetic anisotropy energies Δ Eδγ of surfaces, films, and clusters of Fe, Co, and Ni. The quantitative differences between the approximations allow us to quantify the effects of orbital polarizations on Liδ and Δ Eδγ. One observes that, with an appropriate choice of B, the OP ansatz yields a very good agreement with the rigorous orbital dependent calculations. The simplest orbital independent approach underestimates Liδ and Δ Eδγ systematically. However, it provides a good qualitative description of the main general trends as a function of dimensionality, local environment, and d -band filling. Advantages and limitations of the various approaches are discussed. © 2006 The American Physical Society.

publication date

  • 2006-01-01