Atomic Magnetism

Chemicals are composed of atoms, discrete particles of matter incapable of further subdivision in the course of a chemical reaction. They are the smallest units of an element. Atoms of the same element are identical and equal in weight. All specimens of gold have the same melting point, the same density, and the same resistance to attack by mineral acids. Similarly, all samples of iron of the same history will have the same magnetism. Atoms of different elements have different properties and differ in weight. 

But similar calculations for the iron-group ions show marked disagreement with experiment, and many attempts were made to explain the discrepancies. The explanation is simple in many condensed systems the perturbing effect of the atoms or molecules surrounding a magnetic atom destroys the contribution of the orbital momentum to the magnetic moment, which is produced entirely by the spin moments of unpaired electrons.40... 

Therefore, an atomic model, made of a superposition of independent densities centered at the magnetic atoms, was built. The magnetic structure factor can be written as... 

Figure 3. YCo5 magnetization density of the magnetic atomic model.

Weltner, W. Jr. 1983. Magnetic Atoms and Molecules. New York Van Nostrand Reinhold. Reprinted Mineola, New York Dover Publications, 1989. 

Electro- Magnetic Atomization 600-850 Narrow size distribution Sn, Pb — 0.05- 0.12 Low Narrow size distribution Low volume productivity... 

Kramers, H. A. Interaction between magnetic atoms in a paramagnetic crystal. Physica 1, 182 (1934). 

W. Weltner, Jr., Magnetic Atoms and Molecules, Scientific and Academic ed.. New York, 1983. 

In brief, a magnetic atomic nucleus in a magnetic field may be either lined up with or opposed to the external field, and the transition from one state to the other corresponds to an amount of energy which can be provided by electromagnetic radiation in the radiofrequency range. 

An even more quantitative application of VB theory can be developed from the realization that the nearest-neighbor VB model as developed, for example, by Pauling [10], can be mapped exactly onto a Heisenberg spin Hamiltonian [17]. The Heisenberg spin Hamiltonian has long been used to study the interaction between magnetic atoms in transition metal compounds and other paramagnetic substances [18], and can be written most simply as... 

Small magnetic particles exist in nature or are produced artificially (Chs. 6 to 8). Nanoparticles have sizes ranging from a few nanometers to submicron dimensions (Ch. 7), whereas molecular magnets (Ch. 6) contain a few magnetic atoms in well-defined atomic environments. Clusters are intermediate structures, with less well-defined atomic environments but exhibiting atomic features such as facets (Ch. 8). 

Figure 20 shows a model of two coupled and generally nonequivalent magnetic nanodots or clusters. The dots total spins S and S can be written as S = N S0 and S = N S 0, where N and N are the respective numbers of magnetic atoms per dot. The Hamiltonian of the first dot contains the Zeeman energy - gjUojuBH S and the anisotropy term... 

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