Electronic spin-fluctuation theory of finite-temperature cluster magnetism: Size and environment dependence in FeN Article uri icon

abstract

  • The temperature dependence of the magnetic properties of FeN clusters (N≤24) are determined in the framework of a functional-integral itinerant-electron theory. For each exchange-field configuration ξ, the electronic structure is calculated by using a realistic d -band Hamiltonian and a real-space recursive expansion of the local Green%27s functions. The statistical averages over all ξ are performed by implementing a parallel tempering exchange Monte Carlo method. Results are given for the average magnetic moment per atom μ̄ N, local magnetic moments μl at different atoms l within the cluster, and interatomic spin-correlation functions γlk as a function of temperature T. A remarkable dependence of μ̄ N (T) on size and structure is observed that reflects the importance of the electronic structure to the cluster spin excitations. The correlation between local atomic environment and finite T magnetism is analyzed in some detail by means of the spin-correlation functions. The role of bond-length relaxations on the temperature dependent properties is quantified. An interpretation of our electronic results in terms of Ising or Heisenberg models of localized magnetism reveals a strong dependence of the effective interatomic exchange couplings Jlk on size and local coordination number, which defies straightforward transferability and easy generalizations. © 2009 The American Physical Society.
  • The temperature dependence of the magnetic properties of FeN clusters (N≤24) are determined in the framework of a functional-integral itinerant-electron theory. For each exchange-field configuration ξ, the electronic structure is calculated by using a realistic d -band Hamiltonian and a real-space recursive expansion of the local Green's functions. The statistical averages over all ξ are performed by implementing a parallel tempering exchange Monte Carlo method. Results are given for the average magnetic moment per atom μ̄ N, local magnetic moments μl at different atoms l within the cluster, and interatomic spin-correlation functions γlk as a function of temperature T. A remarkable dependence of μ̄ N (T) on size and structure is observed that reflects the importance of the electronic structure to the cluster spin excitations. The correlation between local atomic environment and finite T magnetism is analyzed in some detail by means of the spin-correlation functions. The role of bond-length relaxations on the temperature dependent properties is quantified. An interpretation of our electronic results in terms of Ising or Heisenberg models of localized magnetism reveals a strong dependence of the effective interatomic exchange couplings Jlk on size and local coordination number, which defies straightforward transferability and easy generalizations. © 2009 The American Physical Society.

publication date

  • 2009-01-01