Mutual Orientation of Electric Intracrystalline and Magnetic Fields in Iron Borate Single Crystals

X-ray structural analysis, Mössbauer spectroscopy, and
ab initio
calculations are used to study the structural properties and refine the orientation of intracrystalline fields in FeBO
₃
crystals in the region of the magnetic phase transition. It is found that in the temperature range of 293–403 K, the trigonal lattice parameters increase monotonically. Analysis of the electron density distribution maps does not show visible local disordering over the entire investigated temperature range. It is found that iron borate has an axially symmetric electric field gradient (EFG) whose main axis is directed along [001]. This orientation is maintained above and below the Néel point. In the magnetically ordered state of the crystal, the main axis of the EFG is orthogonal to the direction of the hyperfine magnetic field at iron nuclei. The results obtained will be used to develop a theoretical model of the formation of hyperfine structure in iron borate, which is important for applications of such crystals in next-generation synchrotron technologies.