MS28-P05 Magnetic Raman scattering and symmetry analysis of complex-structure antiferromagnets Ni2NbBO6 and Fe3BO6Isostructural orthorhombic crystals Ni2NbBO6 and Fe3BO6 belong to the Pnma (#62) space group  and manifest 3D long-range AFM transitions at TN=23.5 K  and TN=508 K, respectively. Such difference in transition temperatures is mostly due to different connectivity; while in Ni2NbBO6 magnetic ions occupy only the general 8d positions, in Fe3BO6 they are located in the 8d and 4c ones, which results in complitely distinct magnetic structures and superexchange paths. Other characteristic feature of Fe3BO6 is a presence of a weak ferromagnetic moment, which is spontaneously reoriented from  to  axis at TSO=415 K. Thereby, these systems offer an unique playground to explore static/dynamic magnetism and symmetry requrements for the existance and orientation of the weak ferromagnetic moment.
We present the experimental results on the crystal growth and studies of both lattice and magnetic dynamics, and their interaction in single crystals of Ni2NbBO6 and Fe3BO6 with the use of the polarized Raman spectroscopy in a wide temperature range 10-550 K. Nontrivial spin-phonon interaction with different signs of coupling constant depending on particular phonon mode was observed at TN. In the AFM phases several magnetic modes of different nature were registered, including two-magnon ones. Methods of magnetic space groups and irreducible representations were used to determine the set of magnetic subgroups compatible with experimental observations. Appropriate Hamiltonians including several isotropic exchange and single-ion anisotropy constants were suggested for describing two-magnon excitations within the linear spin wave theory. Thus we were able to show that magnetic Raman scattering supported by symmetry analysis could be used for determinationof magnetic structures and exchange/anisotropy parameters .
 Ansell, G. B. et al. (1982). Acta Cryst. B 38, 892-893.
 Rao, G. N. et al. (2015). Phys. Rev. B 91, 014423-5.
 Prosnikov M. A. et al. (2017). Phys. Rev. B 96, 014428-10.Keywords: magnetic Raman scattering, symmetry analysis, magnetic space group