Spin-fluctuation energies in transition-metal clusters
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abstract
A functional-integral theory of itinerant magnetism is applied to 3d transition-metal clusters. The low temperature limit of the local spin-fluctuation energies ΔFl(ξ) at different atoms l is determined as a function of the exchange field ξ by using a real-space recursive expansion of the local Green%27s functions. The size, structural, and local-environment dependence of ΔFl(ξ) is calculated for representative examples of FeN and NiN clusters with N ≤ 51 atoms. The interplay between fluctuations of the module and of the relative orientation of the local magnetic moments is analyzed. Module fluctuations generally dominate in the case of NiN, while Fe clusters show a stronger tendency to local moment reversals. A remarkable dependence of the spin-excitation spectrum on the local atomic environment and on interatomic bond-length relaxations is revealed. The transition from simple spin flips to module fluctuations of the local exchange fields is discussed as a function of cluster size.
A functional-integral theory of itinerant magnetism is applied to 3d transition-metal clusters. The low temperature limit of the local spin-fluctuation energies ΔFl(ξ) at different atoms l is determined as a function of the exchange field ξ by using a real-space recursive expansion of the local Green's functions. The size, structural, and local-environment dependence of ΔFl(ξ) is calculated for representative examples of FeN and NiN clusters with N ≤ 51 atoms. The interplay between fluctuations of the module and of the relative orientation of the local magnetic moments is analyzed. Module fluctuations generally dominate in the case of NiN, while Fe clusters show a stronger tendency to local moment reversals. A remarkable dependence of the spin-excitation spectrum on the local atomic environment and on interatomic bond-length relaxations is revealed. The transition from simple spin flips to module fluctuations of the local exchange fields is discussed as a function of cluster size.
