Korringa relation

The most detailed NMR study of impurity band formation in a semiconductor in the intermediate regime involved 31P and 29 Si 7). line width and shift measurements at 8 T from 100-500 K for Si samples doped with P at levels between 4 x 1018 cm 3 and 8 x 1019 cm 3 [189], and an alternate simplified interpretation of these results in terms of an extended Korringa relation [185]. While the results and interpretation are too involved to discuss here, the important conclusion was that the conventional picture of P-doped Si at 300 K consisting of fully-ionized donors and carriers confined to extended conduction band states is inadequate. Instead, a complex of impurity bands survives in some form to doping levels as high as 1019 cm 3. A related example of an impurity NMR study of impurity bands is discussed in Sect. 3.8 for Ga-doped ZnO. 

The main result extracted from P NMR was that the AU55 clusters do not exhibit a normal Korringa relation. Rather, there is an indication of the sort of general two-level behavior often seen in disordered glassy systems. This does not appear to be in disagreement with the results reported above, especially when one considers the modification of the intra-cluster energy levels due to the intercluster interactions. 

The absolute chemical shifts of protons in diamagnetic solids are typically near 30 ppm (28), and the Knight shift caused by conduction electrons through contact interaction is estimated to be —31.2 ppm, using the experimental T1T value of 180 JK-sec and the Korringa relation (29) ... 

For electronic contribution will be used the Korringa relation... 

Ti versus temperature data showing deviations from Korringa-relation. 

HOptner et al.118 have carried out 1FI and 19F SLR time as a function of temperature. Fluorines are known to be relaxed mainly by the reorientational motion of the anions and by the interaction with fixed paramagnetic impurities, the protons are relaxed additionally above 150 K predominantly by highly mobile paramagnetic species, whose concentration could be determined directly via the NMR signal amplitude. Korringa relation observed for proton relaxation shows that it is metallic above 183 K. Further, 1/Ti versus (vL) 1/2 dependence of the proton relaxation supports the ID spin transport and also confirms that only protons of the cation stacks are relaxed by the highly mobile paramagnetic species. 

The spin-lattice relaxation rate, T -1, is due to modulation of the hy-perfine interaction by the electronic spin motion of the conduction electrons and therefore probes the electron dynamics. The (/+S, + I-Si+) term in Hc induces transitions of the nucleus, giving the Korringa relation [21] for a noninteracting electron gas ... 

Eiq.(1) reduces to the Korringa relation even in 10 case, and T is independent of frequency. However, T 1 observed in TTF-TCNQ at room temperature shows the following frequency dependence (see fig.1) T ws for -1... 

The relaxation rate (l/Tj) of H NMR show the Korringa relation above 7).. Far below T, an enhancement of l/Tj was observed in the Cu(NCS)2 and Cu[N(CN)2]Br salts just like P (ET)2l3 but the enhancement is higher. The origin of the l/Tj enhancement is not understood yet, although vortex melting is proposed as one possible origin. C NMR measurements on Cu(NCS)2 and Cu[N(CN)2]X (X = Cl, Br) salts of ET enriched with C at the central C JC bond indicate the same tempo--ature dependence of 7 , among these three salts above 50 K. 

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