Degree of spin polarization

Just as for the simple, spin compensated situation where pa(r) = pp(r) = j p(r), there are related expressions for the exchange and correlation energies per particle of the uniform electron gas characterized by p (r) pp(r), the so-called spin polarized case. The degree of spin polarization is often measured through the spin-polarization parameter... 

The use of LICS in the production of spin-polarized photo-electrons has also been investigated [90]. The general theoretical results have been applied to Rb and Cs. In both cases, enhancement of a factor of 2 in the degree of spin polarization has been obtained by the introduction of a dressing laser at intensity larger than 10 W/cm. ... 

The impurity interacts with the band structure of the host crystal, modifying it, and often introducing new levels. An analysis of the band structure provides information about the electronic states of the system. Charge densities, and spin densities in the case of spin-polarized calculations, provide additional insight into the electronic structure of the defect, bonding mechansims, the degree of localization, etc. Spin densities also provide a direct link with quantities measured in EPR or pSR, which probe the interaction between electronic wavefunctions and nuclear spins. First-principles spin-density-functional calculations have recently been shown to yield reliable values for isotropic and anisotropic hyperfine parameters for hydrogen or muonium in Si (Van de Walle, 1990) results will be discussed in Section IV.2. 

Brunner, Pines and coworkers reported on the enhancement of NMR signals in solid Cgo and C70 using a laser-polarized xenon. NMR signals emanating from surface nuclei of solids may be enhanced by the transfer of spin polarization from laser-polarized noble gases via SPINOE (spin polarization induced nuclear Overhauser effect). The paper describes experiments in which the spin polarization is transferred under MAS from laser-polarized - Xe to a nuclear spin with a low gyromagnetic ratio in the fullerenes Ceo and C70, which are polycrystalline materials with a low surface area. In C70, a different degree of enhancement of the NMR spectrum is observed for the different atomic sites in the molecule. 

The restricted-unrestricted approach not only improves results from the unrestricted approach, but also allows to rigorously describe the effect of spin polarization for tlie hyperfine coupling constants as well as to provide ways to analyze the behavior of spin polarization (response term in RU approach, see fheory part) in problematic cases. The RU approach therefore provides a higher degree of control over the calculation and its analysis compared to the unrestricted formalism. It can consequently be recommended for investigations of hyperfine coupling constants in various molecular systems. 

Thus spin polarized photoemission has been shown to be a new tool in giving information on the surface magnetization. Besides, efficient sources of spin polarized electrons can be made from e.g. EuO containing a few percent La and degrees of polarization of 80% at 30 kOe have been verified experimentally. 

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