Resonance linewidth, concentration effect

Similarly to the ESR of the lanthanide ions in insulators, in metallic systems ESR contributes to understanding of the spectroscopic state of the ion in the host lattice and the symmetry and magnitude of the crystalline electric field at the lanthanide site. The g-shift of the resonance may be related to the sf exchange interaction and the spin polarization of the conduction electrons, and the temperature and concentration dependence of the g-shift and resonance linewidth relate to the bottleneck effect in the spin relaxation process. These relationships have been outlined in section 3.5. 

Finally, Dodds and Sanny (1978) observed the Er resonance in polycrystalline films which were deposited at room temperature onto fiised-quartz or plexiglass substrates at pressures of approximately 1 x 10" Torr. The nominal erbium concentration varied between 0.2 and 2%. The angular variation of the g-value and linewidth was measured for each sample at a fixed temperature in the liquid He range. During cooling, the difference in thermal contraction between film and substrate produced an effective uniaxial strain in the film. The contraction of the substrate forces the film to expand in the direction perpendicular to the substrate, which becomes the preferred axis and the g-value will depend on the orientation of the field with respect to this axis. In this way even in polycrystalline films an anisotropy of the g-value can be observed. The inferred orbit-lattice coefficients were somewhat smaller than those observed in insulators. They were the same for films on quartz or on plexiglass substrates. This fact supports the conclusion that the strain is macroscopically uniform in contrast to the argumentation of Arbilly et al. (1975). 

In the La-H system, the proton diffusive motion also has significant effects on the linewidth, relaxation time T, and Knight shift of the La resonance via the nuclear quadrupole interaction of the La with the fluctuating electrostatic environment resulting from the proton motion. All of these parameters of the La spectrum are strongly temperature and concentration dependent. Schreiber and Cotts (1963) show in detail that the La data confirm and support the model of proton diffusion based on the proton NMR results alone. 

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