Excess relaxation rate definition

Figure 2. Graph showing the excess relaxation rate (I/T2) of the dominant NMR signal in a system where the observed nucleus is undergoing chemical exchange between two sites, A and B. The mole fraction of nuclei in site B, pg, is much less than that of site A, p. The definitions of n and are given by eqs. 5 and 6 (from Ref. 1). (with permission from Springer Verlag)...

At r > 5K, the muon spin relaxation rate becomes unmeasurably small (i.e., A < 0.004 (xs ). Taking the high-temperature value of the moment on Ce one arrives at a spin fluctuation rate in excess of 10 Hz. In particular, no effect on A could be seen around 10 K where susceptibility reaches a peak. This definitely proves that this peak is not connected to any magnetic transition, but signals the onset of the AFM spin correlations seen in the neutron measurements mentioned. [tSR, due to its different time window, responds only when the correlations have caused a substantial slowing down of spin fluctuations (i.e., at much lower temperatures). 

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