Suppression of the Cycloidal Spin Arrangement in BiFeO₃ Caused by the Mechanically Induced Structural Distortion and Its Effect on Magnetism

Bismuth ferrite (BiFeO₃) particles are prepared by a combined mechanochemical−thermal processing of a Bi₂O₃ + α-Fe₂O₃ mixture. Structural, magnetic, hyperfine, morphological and chemical properties of the as-prepared BiFeO₃ are studied using X-ray diffraction (Rietveld refinement), ⁵⁷Fe Mössbauer spectroscopy, SQUID magnetometry, electron microscopy and energy dispersive X-ray spectroscopy. It is revealed that the structure of the ferrite exhibits the long-range distortion (significantly tilted FeO₆ octahedra) and the short-range disorder (deformed FeO₆ octahedra). Consequently, these structural features result in the suppression of a space modulated cycloidal spin arrangement in the material. The latter manifests itself by the appearance of only single spectral component in the ⁵⁷Fe Mössbauer spectrum of BiFeO₃. The macroscopic magnetic behavior of the material is interpreted as a superposition of ferromagnetic and antiferromagnetic contributions with a large coercive field and remanent magnetization. Taking into account the average particle size of the as-prepared BiFeO₃ particles (∼98 nm), exceeding the typical period length of cycloid (∼62 nm), both the suppression of the spiral spin structure in the material and its partly ferromagnetic behavior are attributed to the crystal lattice distortion caused by mechanical stress during the preparation procedure.