Electron paramagnetic resonance dynamic susceptibility

Since its discovery by Zavoisky in 1944, electron spin resonance spectroscopy (ESR) (also called electron paramagnetic resonance spectroscopy [EPR]) has become an essential tool for the study of the structure and dynamics of molecular systems containing one or more unpaired electrons. Such paramagnetic systems can frequently be examined using magnetic susceptibility techniques as well, but these do not provide the detailed information that ESR spectroscopy does. ESR spectroscopy and magnetic susceptibility methods each have their strengths and limitations and often provide complementary information. 

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. 

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