Peculiar Features of the Spectrum Saturation Effect When the Spectral Diffusion Operates: System with Two Frequencies

The saturation of a spectrum with two separated spectral lines is theoretically analyzed in the presence of the spectral diffusion. Surprising effects of circularly polarized alternating magnetic field on the spectrum under saturation conditions were obtained. The alternating magnetic field pushes two lines apart, while the spectral diffusion tends to shift the lines to the center of gravity. As a result, the so-called exchange narrowing of the spectrum occurs at a higher spectral diffusion rate with the increase in the amplitude of the alternating magnetic field. The spectrum is presented as a sum of two lines which correspond to the two independent collective modes of the magnetization vectors motion. The resonance frequencies of these modes depend on the spectral diffusion rate and the intensity of the alternating magnetic field.