Substitution driven structural and magnetic properties and evidence of spin phonon coupling in Sr-doped BiFeO3 nanoparticles

Abstract

The manifestation of dimensionalities and Sr induced modifications in structural, vibrational and magnetic properties of Bi_1−xSr_xFeO₃; (x = 0–0.25) nanoparticles synthesized by a tartaric acid based sol–gel route are reported. X-ray diffraction and electron microscopy studies reveal the phase purity and nanocrystalline nature (45–90 nm) of Bi_1−xSr_xFeO₃ samples. The Sr ions substitution motivated the coexistance of rhombohedral (R3c) and pseudo tetragonal (P4/mmm) structural symmetry for the x = 0.25 sample which leads to enhancement of saturation magnetization due to the distorted cycloid spin structure and uncompensated surface spins, which is in concomitance with the electron paramagnetic resonance (EPR) and Mössbauer studies. The ferromagnetic ordering contribution continuously increases with increasing Sr content from x = 0–0.25 samples with a maximum saturation magnetization of 0.72 emu g⁻¹ for the x = 0.25 sample which is also endorsed by second order Raman modes. X-ray photoelectron and Mössbauer measurements confirmed the dominance of the Fe³⁺ oxidation state. Alteration in QS hyperfine parameters and line-width analysis have been probed by Mössbauer analysis with increasing Sr content in BiFeO₃ nanoparticles suggesting the destruction of the spin cycloid.