Magnetic resonance of intrinsic defects in the spin-Peierls magnet CuGeO3

Magnetic resonance in pure single-crystal CuGeO 3 at frequencies 9–75 GHz in the temperature range 1.2–25 K is investigated. Splitting of the magnetic-resonance line into several spectral components is observed at temperatures below 5 K, where spin-Peierls dimerization suppresses the magnetic susceptibility and the ESR signal intensity. Analysis of the magnetic resonance spectra over a wide frequency range with different directions of the magnetic field at different temperatures makes it possible to identify among these components the ESR signals due to defects, having effective spin S =1/2 and spin S =1, in the spin-Peierls phase. The g factor corresponding to these ESR signals is the same and close to the value characteristic for the ion Cu 2+ . Another magnetic-resonance line is characterized by a strongly anisotropic g factor and an increase (at a threshold in the excitation power) in the susceptibility both at resonance and in the line wings. These signals are tentatively attributed to two possible types of planar defects arising on the walls of domains of the spin-Peierls state with different values of the dimerization phase.