Spin modulation of 57Fe NMR frequency and relaxation in BiFeO3

NMR spectra were measured in 57Fe enriched ferroelectric-antiferromagnet BiFeO3 with space modulated magnetic structure of cycloidal type. This structure leads to space modulation of local field on 57Fe nuclei as well as space periodic spin-spin relaxation and specific NMR line shape with frequency variable local width. Line shape temperature behavior is described using the model of nuclei in Bloch walls. This effect is based on indirect Sule-Nakamura spin-spin interaction which becomes effective at high concentration of magneto-active nuclei as a consequence of excitement of spin waves