Crystalline field Strong

Strong crystalline field Hso < H e < Hqf- In this approach, the crystalline field term dominates over both the spin-orbit and the electron-electron interactions. This applies to transition metal ions in some crystalline environments (see Section 6.4). 

One of the simplest descriptions of the crystalline field occurs for the d outer electronic configuration (i.e., for a single d valence electron). This means that //ee = 0 and, consequently, there is no distinction between intermediate and strong crystalline fields. 

In strong crystalline fields or highly distorted fields a doublet S= state becomes lowest in energy. In this situation there are generally no nearby states, so that g factors are close to 2.0023 and the ESR is observed at higher temperatures. The ESR results can be fitted to Eq. (171) and observed values for the spin Hamiltonian parameters are given in Table XVI. 

On a strong self-organizing nature of liquid crystals, spontaneous formation of nano-structure in molecular aggregation is also an important issue in research as an origin of superfunctionality in molecular materials. Recent studies on how to build-up such nano-structure in organic materials have shown the importance of application of liquid crystalline field. Molecular dynamics (MD) simulation has been applied to this issue [10] and the wider variation in experimental approaches has been seen [11] in recent years. 

T) and a reduction in field magnitude is due to the influence of Beep and (here probably to a minor degree) of B,i,f as discussed for Eu compounds in section 5.1.1. In contrast, for Np + the orbital field dominates and all other contributions are of little importance. The average value of in the silicides is 0.6B f. This is quite close to what one expects if crystalline electric field interactions put the Ej level lowest. As shall be seen further below this crystalline field situation is strongly evidenced in the magnetic behavior of NpCr2Si2. 

A variety of structural information can be inferred from magnetic susceptibility data. " The site symmetry of a paramagnetic ion can be determined from the localized atomic moment. The orbital contribution to atomic moment is strongly influenced by the crystalline fields, and therefore magnetic susceptibility measurements provide information about the local symmetry of the ions. For example, Co ions have a nearly spin-only atomic moment of in a tetrahedral interstice, whereas octahedrally coordinated Co has a moment of about 3.7 Ub. 

Polymer Ferroelectrics. In 1969, it was found that strong piezoelectric effects could be induced in the polymer poly(vinyhdene fluoride) (known as PVD2 or PVDF) by apphcation of an electric field (103). Pyroelectricity, with pyroelectric figures of merit comparable to crystalline pyroelectric detectors (104,105) of PVF2 films polarized this way, was discovered two year later (106.)... 

Coercivity of Thin-Film Media. The coercivity ia a magnetic material is an important parameter for appHcations but it is difficult to understand its physical background. It can be varied from nearly zero to more than 2000 kA/m ia a variety of materials. For thin-film recording media, values of more than 250 kA / m have been reported. First of all the coercivity is an extrinsic parameter and is strongly iafluenced by the microstmctural properties of the layer such as crystal size and shape, composition, and texture. These properties are directly related to the preparation conditions. Material choice and chemical inborn ogeneties are responsible for the Af of a material and this is also an influencing parameter of the final In crystalline material, the crystalline anisotropy field plays an important role. It is difficult to discriminate between all these parameters and to understand the coercivity origin ia the different thin-film materials ia detail. 

A from the surface the density is typically constant and equal to the bulk value. In strong unscreened electric fields several authors [137-140] report a phase transition towards a ferroelectric crystalline state in their simulations. However, it should be kept in mind that these systems, because of the absence of ionic screening, are rather unphysical in nature. 

Electro-optic The liquid crystal plastics exhibit some of the properties of crystalline solids and still flow easily as liquids (Chapter 6). One group of these materials is based on low polymers with strong field interacting side chains. Using these materials, there has developed a field of electro-optic devices whose characteristics can be changed sharply by the application of an electric field. 

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