In this work, high-resolution triple-crystal X-ray diffraction
and reciprocal space mapping were applied to study the effect of magnetoelastic
interactions on the structural perfection and diffraction properties
of magnetically ordered iron borate crystals. It was established that
the presence of magnetic domains with different orientation of magnetization
and near-surface magnetism effect in FeBO3 leads to the
appearance of disordered areas in crystals and slight changes in the
lattice parameters. This is affected in the broadening or splitting
of the reciprocal lattice point and diffraction properties of the
crystal. An applied weak external magnetic field alters the domain
structure and significantly improves the diffraction characteristics
of FeBO3 crystals. This effect is important for practical
applications of iron borate crystals, including the use of these crystals
as X-ray modulators.