Raman Spectroscopy and DFT Study of Spin‐Reorientation Transition in the Nickel‐Cobalt Orthoborates

ABSTRACT Nickel‐cobalt oxyborates (Ni,Co) 3 B 2 O 6 with a kotoite‐type orthorhombic structure are known as antiferromagnetic materials and are of interest for optical applications and as promising battery anode materials. We report and analyze the results of experimental low temperature Raman studies of the phonon spectra measured in some polarizations of the Ni 3 B 2 O 6 , Ni 2.81 Co 0.19 B 2 O 6 , Ni 2.4 Co 0.6 B 2 O 6 , Ni 2.07 Co 0.93 B 2 O 6 , and Co 3 B 2 O 6 crystals. Simulations of the density functional theory of Raman spectra of the Ni 3 B 2 O 6 and Co 3 B 2 O 6 crystals have been performed and analyzed. The vibrational modes of the Ni 3 B 2 O 6 and Co 3 B 2 O 6 crystals were interpreted. Low‐wavenumber modes in the Raman spectra are associated with Ni and Co atoms vibrations accompanying BO 3 group deformations. Clear evidence of spin‐phonon interaction was found for some specific phonons below . The anomalies in the behavior of these phonon modes as a function of the nickel concentration in the crystal have been presented. The position and intensity of the Raman modes decrease when the Ni atoms are replaced by Co atoms.