Korringa relaxation

Perhaps not surprisingly, the most thorough NMR studies of Knight shifts, Korringa relaxation, metal-insulator transitions, and the NMR of the dopant nuclei themselves have been carried out for doped silicon. Since few semiconductors other than PbTe, which presents a considerably more complicated case, have been studied in such detail, it is worthwhile here to summarize salient points from these studies. They conveniently illustrate a number of points, and can shed light on the behavior to be expected in more contemporary studies of compound semiconductors, which are often hindered by the lack of availability of a suite of samples of known and widely-varying carrier concentrations. 

The second argument offered in [359] was based on the observation of 71Ga / j 1 rates at different temperatures that were faster than those calculated assuming Korringa relaxation as the only mechanism. However, this observation cannot be used to exclude the presence of Korringa relaxation, since additional mechanisms can always contribute additively to relaxation rates. Indeed, exactly such behavior has been observed for 71Ga MAS-NMR of h-GaN co-doped with Ge and Mn, where... 

On implantation into the cold foil the nuclei are initially fhot i.e. unpolarised. They approach thermal equilibrium with the foil lattice temperature through the Korringa relaxation mechanism via the conduction electrons. 

In determiifing whether a small particle is metallic, it is not practical to attach wires and measure a conductivity. However, conductivity, Pauli susceptibility, Kifight shift, and Korringa relaxation all rely on the same... 

Other experimental method at a eomparable level of detail, although in some eases the conclusions reached support previous work by XANES using synchrotron radiation. Our results clearly demonstrate that due to a quantum mechanical electron density spillover from platinum, the interface is metallized, as evidenced by Korringa relaxation and Knight shift behavior. Thus, the adsorbate on a platinum electrode belongs to the metal part of the platinum-solution interface, and most likely other d-metal interfaces, and should be considered as such in any realistic models of the structure of the electrical double layer of interest to electrocatalysis. 

Fig. 61. Temperature dependence of the TF muon spin depolarization rate in ErAlj for different fields. Left Fit to the low-temperature region. Right Fit to the high-temperature region. The fit functions are explained in the text. / Ai(0) is a parameter of Korringa relaxation. From Hartmann et al. (1986).

Equation (4) corresponds to the Korringa relaxation , which is well known in nuclear magnetic resonance (NMR) spectroscopy in metals. 

Fig. 42. Schematic temperature dependence of the linewidth in HFS (full line) contributions due to the onsite Korringa relaxation Aff (narrow-dashed line) and inter-site spin fluctuations Afff (long-dashed line) are indicated separately. The parameters that have been used in these calculations are indicated in the text.

Fig. 43. Temperature dependence of the Gd-ESR linewidth in CeCu2Si2 (diamonds) and in LaCu2Si2 (solid line). The dashed line indicates the Korringa relaxation in the heavy Fermi-liquid regime. The points shown as triangles were obtained by subtraction of AH(T) as determined in LaCu2Si2 from AH(T) of CeCu2Si2 and are estimates of the pure intersite effects. From Elschner and Schlott (1988).

Later on Cieplak et al. (1993) explained the increase of the linewidth towards low temperatures in terms of critical phenomena which are expected close to a spin-glass phase, and the broadening of the Fe EPR line was attributed to the freezing-in of spin fluctuations. The broadening of AH towards high temperatures was attributed to Korringa relaxation processes. Cieplak et al. (1993) reported a Korringa slope which is almost independent of the Fe concentration for 0.004 < 0.03, which is hard to understand... 

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