ESR and longitudinal response in metals containing localized paramagnetic centers with spinS>1/2

Abstract

The theory deseribing electron spin resonance (ESR) and the longitudinal magnetization response of coupled spin systems in a metal eontaining both delocalized conduction electrons ("espins") and localized paramagnetic eenters ("s-spins") is generalized to the case of arbitrary halfinteger spin value, S > 1/2, of the s-spins. The consideration is based on the Bloch-Hasegawa equations supplemented by taking into account the coupled evolution of the longitudinal magnetization components and the effect of weak ESR saturation by the microwave field. The ESR transversal susceptibility and longitudinal magnetization response are worked out in terms of normal modes related to the coupled s-and e-spin oseillators taking into account the ESR fine strueture (FS) of the sspins. These modes are characterized by effeetive (renormalized) frequencies and relaxation rates (deeays) which differ from the partial ones. In the specific cases of a well-resolved FS (in the isothermal limit) and of the relaxational collapse of the FS due to strong exchange coupling between the s-and e-spins (in both the isothermal and bottleneeked limits), the analytieal expressions are de-¡ which ate relevant to the modulation technique of measuring extremely fast spin-lattice relaxation times in metals.

Saturation Effects in the Magnetic Resonance of Paramagnetic Impurities in Metals

“…This means one must have a distinct paramagnetic resonance well separated from the conduction electron resonance. The analysis of the coupled conduction electron spin -paramagnetic ion resonance remains a challenging but distinct problem with progress continuing to be made [4].…”