Visualization of the magnetic domain structure in FeBO$_3$ and Fe$_{0.94}$Ga$_{0.06}$BO$_3$ single crystals by synchrotron X-ray topography

The method and experimental cell for the X-ray diffraction diagnostic of crystalline materials exposed to magnetic fields have been described. It has been shown that the application of even weak magnetic fields (about several Oersteds) allows one to significantly reduce the diffraction contrast on X-ray topograms of FeBO$_3$ and Fe$_{0.94}$Ga$_{0.06}$BO$_3$ single crystals, which is due to a nonuniform distribution of magnetostriction strains, and thereby to improve the degree of their structural perfection. The magnetic domain structure of Fe$_{1 -x}$Ga$_x$BO$_3$ solid solution single crystals has been visualized. It has been found that small concentrations of diamagnetic Ga ions do not significantly change the configuration of domain walls in FeBO$_3$-based crystals.