Raman Spectroscopy, Dynamical and Nonlinear Optical Properties of Multicomponent Garnet (Eu, Gd, Dy, Er, Y) ₃ Fe ₅ O ₁₂ : A Combined Experimental and Computational Study

ABSTRACT The article presents the results of a combined experimental and computational study by DFT methods of Raman and Mössbauer spectra, dynamical and nonlinear optical (NLO) properties of single‐component and multicomponent garnets Y 3 Fe 5 O 12 (YIG), LnIG (Ln = Eu, Gd, Dy, Er), and (Y 0.2 Gd 0.2 Er 0.2 Eu 0.2 Dy 0.2 )IG (YLnIG), synthesized by glycine–nitrate pyrolysis. The Raman band assignments to fundamental vibrational modes were held using an analysis of experimental data with the support of phonon spectra ab initio calculations. It was shown that displacements of all atoms except Fe in octahedra are involved in Raman active vibrational modes. The most intensive Raman bands are attributed to phonon modes related to atomic displacements in FeO 4 tetrahedra. Raman spectra measurements performed for YIG and YLnIG garnets in the temperature and pressure ranges of 83–773 K and 0–13 GPa revealed their structural stability with the absence of any phase transition fingerprints. The analysis of temperature and baric behavior of vibrational modes disclose that the value of anharmonicity in multicomponent garnet YLnIG is of the same magnitude as the one in single‐component YIG. The values of thermal expansion coefficients were estimated to be equal to 11.07·10 −6 and 10.20·10 −6 K −1 for YLnIG and YIG garnets respectively. The nonlinear properties of YIG and EuIG garnets were studied theoretically using the CPHF approach; the values of nonzero susceptibility tensor components were characterized by high values of diagonal components: the values were equivalent to = 35.8·10 −22 and 38.4·10 −22 m 2 /V 2 and = 9.04·10 −22 and 9.10·10 −22 m 2 /V 2 , respectively, for YIG and EuIG.