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Disorder of (FeO5)-O-(2) bipyramids and spin-phonon coupling in SrFe12O19 nanoparticles
Authors: Buzinaro, MAP; Macedo, MA; Costa, BFO; Ferreira, NS
Ref.: Ceram. Int. 45(10), 13571-13574 (2019)
Abstract: The local structure of SrFe 12 O 19 nanoparticles was investigated by a combined synchrotron pair distribution function (PDF), Raman and ⁵⁷ Fe-Mössbauer spectroscopic analysis. The PDF and ⁵⁷ Fe-Mössbauer spectroscopy results indicate that SrFe 12 O 19 nanoparticles exist in an M-type hexagonal phase (∼10 nm), with a dynamically disordered trigonal bipyramidal Fe(2) site (2b). We determine that at 300 K, the timescale dynamics of Fe ³⁺ ions near the 2b positions are between 10 ⁻¹⁵ and 10 ⁻ s. The Raman spectra show anomalous shifts in all active phonon wavenumbers above T N ≈ 720 K, indicating the presence of spin-phonon coupling. The Fe ³⁺ (2b) dynamic regime motion was interpreted by taking into account changes in the electric polarization at T = T N , which discontinuously drops to zero at this temperature.
