Spin fluctuation frequenc

A preliminary report (Amato et al. 1998) presents ZF- and LF-pSR data down to 0.1K. The ZF spectra are characterized by nuclear-electronic double relaxation. The nuclear part can be suppressed in LF = 20 G. No magnetic transition was observed. Below 10 K, the electronic relaxation rate increases monotonically with decreasing temperature. Application of LF = 200 G also suppresses electronic relaxation, indicating rather slow dynamics of the spin system. From the field dependence of relaxation rate the spin fluctuation frequency was found to be V4f(r —> 0) 2.7 MHz. It appears that this is another case where spin correlations develop at low temperatures, but persistent slow spin dynamics prevent the formation of an ordered magnetic state (see CeNiSn in sect. 9.2 for comparison). 

Here, ojr is the rate of spinner rotation. I is the proton spin number, 8 is the chemical shift anisotropy (CSA) and q is the asymmetric parameter of the CSA tensor. Thus, the line broadening occurs when an incoherent fluctuation frequency is very close to the coherent amplitude of proton decoupling monotonously decreased values without such interference in Figure 1. 

Figure 6. The proton(I)-carbon(S) dipolar coupling during a C-13 T,p and decoupled Tj experiment are compared. The relaxation rate is determined by the molecular fluctuation at the spin lock frequency u>,c or decoupling frequency a,a-...

In spin-lattice relaxation, the excited nuclei transfer their excitation energy to their environment. They do so via interaction of their magnetic vectors with fluctuating local fields of sufficient strengths and a fluctuation frequency of the order of the Larmor frequency of the nuclear spin type. Depending upon the atomic and electronic environment of a nucleus in a molecule and the motion of that molecule, there are five potential mechanisms contributing to spin-lattice relaxation of the nucleus. 

Consider now the influence of the high-frequency fluctuations in the environment only (is 3> B). Since the frequencies of the fluctuations are much higher than the typical spin-dynamics frequencies, one may eliminate these high-frequency fluctuations using the adiabatic (Born-Oppenheimer) approximation, as described, e.g., by Leggett et al. [8]. 

The main equation for the d-electron GF in PAM coincides with the equation for the Hubbard model if the hopping matrix elements t, ) in the Hubbard model are replaced by the effective ones Athat are V2 and depend on frequency. By iteration of this equation with respect to Aij(u>) one can construct a perturbation theory near the atomic limit. A singular term in the expansions, describing the interaction of d-electrons with spin fluctuations, was found. This term leads to a resonance peak near the Fermi-level with a width of the order of the Kondo temperature. The dynamical spin susceptibility in the paramagnetic phase in the hydrodynamic limit was also calculated. 

A simple physical picture that is consistent with the above results is that above T one has coherent itinerant quasiparticle behavior over the entire Fermi surface, observed as an anomalous Fermi liquid. Below T one loses that coherent behavior for a portion of the Fermi surface near the antinodes the hot quasiparticles (those whose spin-fluctuation-induced interaction is strongest) found there enter the pseudogap state its formation is characterized by a transfer of quasiparticle spectral weight from low to high frequencies that produces the decrease in the uniform spin susceptibility below T. The remainder of the Fermi surface is largely unaffected. 

Rotational motion exerts fluctuating magnetic fields on the electron spin and also averages the various tensor components (see Fig. 2). Nitro-xide EPR spectra are profoundly influenced by the rate of this motion relative to the range of electron spin precession frequencies within each hyperfine line. Thus, one can use EPR spectroscopy to determine tr accurately. There are distinct temporal regimes in which spin label spectra require different types of data collection methods and data analysis to achieve this. These regimes are discussed below. 

Accordingly, it is concluded that the NMR signals of [l- C]Val and He residues among a variety of [l- C]amino-acid residues can serve as the most appropriate probes, to examine the local conformation and dynamics of bR from PM especially at the surface area. Otherwise, it should be anticipated that the carbonyl NMR signals are not fully visible from those located at the membrane surface (Ala, Leu, Phe, and Trp), because of interference between the fluctuation frequency and the frequency of magic angle spinning. 

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