Transition-metal clusters magnetism

One of tire interesting aspects of transition-metal clusters is tlieir novel magnetic properties [91, 92, 93 and 94l]. ... 

Pastor G M, Dorantes-Davila J and Bennemann K H 1989 Size and structural dependence of the magnetic properties of small 3d-transition metal clusters Phys. Rev. B 40 7642... 

Size and Structural Dependence of the Magnetic Properties of 3d Transition Metal Clusters. 

Orbital Magnetism in Transition Metal Clusters From Hund s Rules to Bulk Quenching. 

Magnetic-Nonmagnetic Transition in fee 4d-Transition-Metal Clusters. 

The accurate quantum mechanical first-principles description of all interactions within a transition-metal cluster represented as a collection of electrons and atomic nuclei is a prerequisite for understanding and predicting such properties. The standard semi-classical theory of the quantum mechanics of electrons and atomic nuclei interacting via electromagnetic waves, i.e., described by Maxwell electrodynamics, turns out to be the theory sufficient to describe all such interactions (21). In semi-classical theory, the motion of the elementary particles of chemistry, i.e., of electrons and nuclei, is described quantum mechanically, while their electromagnetic interactions are described by classical electric and magnetic fields, E and B, often represented in terms of the non-redundant four components of the 4-potential, namely the scalar potential and the vector potential A. 

In present-day quantum chemistry the Heisenberg Spin Hamiltonian is widely applied for the description of magnetic coupling in transition-metal clusters and may read in the case of a many-electron system,... 

The application of these rules may fail for the prediction of magnetic coupling in transition-metal clusters, where the molecular orbitals may be different from simple atomic d-orbitals and a simple ligand field analysis may not reflect the correct energy splittings. 

In molecules, the interaction of surrogate spins localized at the atomic centers is calculated describing a picture of spin-spin interaction of atoms. This picture became prominent for the description of the magnetic behavior of transition-metal clusters, where the coupling type (parallel or antiparallel) of surrogate spins localized at the metal centers is of interest. Once such a description is available it is possible to analyze any wave function with respect to the coupling type between the metal centers. Then, local spin operators can be employed in the Heisenberg Spin Hamiltonian. An overview over wave-function analyses for open-shell molecules with respect to local spins can be found in Ref. (118). 

Several recent studies have been devoted to understanding and predicting the magnetic and spectroscopic properties of oligonuclear transition metal clusters, concentrating particularly on... 

The University of Montreal showed much foresight with the appointment of Dennis Salahub in 1976. In the next two decades he made several key contributions to the development and applications of density functional (DF) methodology. His early work with the Xa method22 helped to explain diverse complex phenomena in the area of transition metal clusters, their electronic and magnetic properties, and their use as models for chemisorption and catalysis. Explanations emanating from calculations on the reduction of surface mag-... 

Of particular interest are the predicted magnetic moments and the question of whether or not isomers of transition metal clusters can be separated using inhomogeneous magnetic fields. To date, cluster isomers have only been detected via their different chemical reactivity (70-73). One would expect abnormally large magnetic moments for the Ih clusters if they had unusually high density of states at the Fermi level, as has been postulated for aluminum (74)-... 

If the octahedral and icosahedral 13-atom nickel clusters are representative, an inhomogeneous magnetic field is not a good tool for separating isomers of transition metal clusters. This result is reminiscent of the fact that geometry plays no strong role in the ionization potential variation of alkali clusters (80). However, many calculations must be made before we can be definitive here. 

The electronic state calculations of transition metal clusters have been carried out to study the basic electronic properties of these elements by the use of DV-Xa molecular orbital method. It is found that the covalent bonding between neighboring atoms, namely the short range chemical interaction is very important to determine the valence band structure of transition element. The spin polarization in the transition metal cluster has been investigated and the mechanism of the magnetic interaction between the atomic spins has been interpreted by means of the spin polarized molecular orbital description. For heavy elements like 5d transition metals, the relativistic effects are found to be very important even in the valence electronic state. 

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