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

Abstract

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.

Vacancies' effect on the ferroelectric and magnetic response of Eu‐doped Bi0.85Pr0.15Fe0.97Mn0.03O3 thin films

“…We attribute this phenomenon to the superexchange‐interaction phenomenon between cations of the perovskite structure, which produces canted spins reorientation when the Eu increases in the solid solution. Therefore, the octahedral tilting angles change, 51 reducing thus the symmetry from tetragonal to rhombohedral, which is consistent with the XRD results.…”

A Unique Mechanochemical Redox Reaction Yielding Nanostructured Double Perovskite Sr2FeMoO6 With an Extraordinarily High Degree of Anti-Site Disorder

“…This variation is associated with the presence of strongly deformed FeO 6 octahedra in the mechanosynthesized perovskite, as it is derived from the low-temperature 57 Fe Mössbauer spectra presented in Figure 4 . Note that the broadly distorted geometry of the constituent structural units (building blocks) is typical for nanosized particles prepared by mechanochemical routes, and it has been evidenced by nuclear spectroscopic methods in numerous far-from-equilibrium complex oxides ( Šepelák et al, 2009 ; Šepelák et al, 2013 ; Da Silva et al, 2021 ). This is also in line with previous work on Sr 2 FeMoO 6 , where an important crystallographic distortion around Fe 3+ cations is postulated due to highly unspherical electric fields generated by anti-side disorder ( Greneche et al, 2001 ) or, alternatively, due to the existence of Mo vacancies ( Chmaissem et al, 2000 ).…”

Magnetic Behaviour of Perovskite Compositions Derived from BiFeO3

“…An enhancement of ferromagnetism in BiFeO 3 can also be achieved by reducing crystallite size into the nanometre scale when the size becomes comparable with the AFM cycloid period of ~62 nm [43,44]. However, the FM contribution may be enhanced by mechanically induced distortions even in larger BiFeO 3 crystallites [45] (as revealed from significant hysteresis in the magnetization loops similar to those shown in Figure 5) when the material is prepared using the mechanochemical synthesis. Such an observation would point to the critical role of the high-pressure synthesis procedure of BiFe 1−y B 3+ y O 3 perovskite solid solutions introducing mechanical strain and affecting the magnitude of uncompensated magnetic moments in initial cycloidal AFM arrangement.…”