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

Klebson Lucenildo Da Silva,Vladimír Šepelák,Marta Harničárová,Dirk Menzel,Mariia Holub,Rodolfo Bezerra Da Silva,Martin Fabián,Klaus Dieter Becker,Vladimír Girman,Rafael Santiago Trautwein,Olha Skurikhina,Erik Čižmár,Horst Hahn

doi:10.3389/fmats.2021.717185

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.

Highlights

Multiferroics have been the focus of numerous investigations because of their fascinating properties and potential applications
Rietveld analyses of the X-ray diffraction (XRD) data reveal that the patterns are well-fitted using a single rhombohedral phase (ICSD collection code 8823) with space group R3c
As a consequence of the lattice shrinkage, the neighboring FeO6 octahedra in the crystal lattice of the as-prepared BiFeO3 exhibit a relatively small tilting angle of 127.2° (Figure 3B)

Summary

Introduction

Multiferroics have been the focus of numerous investigations because of their fascinating properties and potential applications. BiFeO3 has attracted considerable attention due to its unique multiple functionalities (Castillo et al, 2013). It exhibits a strong coupling of electric, magnetic, and structural order parameters, giving rise to simultaneous ferroelectricity, antiferromagnetic G-type order at reasonable high temperatures, and ferroelasticity (Park et al, 2007; Da Silva et al, 2011; Bai et al, 2005). The spin ordering manifests itself as an incommensurate cycloidal structure with a typical wavelength (λ) of about 62 nm along the hexagonal [001]-axis. The antiferromagnetic vector is locked within the cycloid, averaged to zero over λ (Bai et al, 2005)

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Results

Conclusion