LOW-FREQUENCY DETECTED EPR - PRINCIPLES AND APPLICATIONS

The experimental works described are performed by the authors over las t two decades by means of the LFD EPR technique. The essence of this m ethod is low-frequency detection of the longitudinal spin magnetizatio n while the magnetic resonance is excited by a strong microwave field. The first kind of LFD EPR is the enchanced longitudinal susceptibilit y effect (ELSE) which has been elaborated and applied to study spin th ermodynamics in solids since 1972. Various applications of ELSE are de scribed such as direct measuring of the spin-spin interaction temperat ure T-ss in the course of resonance saturation, spin-lattice and cross relaxation, dynamic nuclear polarization etc. Another version of LFD EPR was employed to study electron spin-lattice relaxation of paramagn etic centers in high-temperature superconductors (HTSC). Recent experi mental data are presented on the electron spin-lattice relaxation of C u(2+)ions in YBa2Cu3O6+x at various temperatures and x values.