Field-induced spin cycloidal modulation to antiferromagnetic transition and possible flexomagnetic effect in BiFeO3 nanoparticles

Ikbel Mallek Zouari (1) , W. Ben Taazayet (1) , J.-M. Grenèche (2) , Lotfi Bessais (3) , B. Dkhil (4) , N. Thabet Mliki (1)

1 département de physique de la faculté des sciences de Tunis
2 IMMM - Institut des Molécules et Matériaux du Mans
3 ICMPE - Institut de Chimie et des Matériaux Paris-Est
4 SPMS - Laboratoire Structures, Propriétés et Modélisation des solides

Beyond its various properties, the model multiferroic BiFeO3 (BFO) displays a rich magnetic structure illustrated in the bulk by its long period (∼62 nm) spin cycloidal modulation. Here, BFO nanoparticles are produced by a facile hydrothermal method and show average size of 8 nm and a narrow size distribution, as determined using x-ray diffraction analysis and transmission electron microscopy images. Mössbauer spectrometry (MS) unambiguously reveals that a cycloidal modulation does still exists with particles about 5 times smaller than the bulk cycloid. Combining macroscopic magnetic measurements and in situ Mössbauer spectrometry, we demonstrate that a critical magnetic field of ∼0.2 T destabilizes the cycloidal modulation to lead to a homogenous antiferromagnetic state, as the result of magnetic anisotropy due to magnetoelastic and surface-confinement effects. More interestingly, further increasing of the external magnetic field up to 8 T does not change the average magnetic hyperfine field and results into multiple Mössbauer sextets we propose to explain by a flexomagnetic effect i.e. magnetic anisotropies resulting from strain gradients due to a continuous variation of the coupling between magnetization and the structural distortion from the surface to the particle core.

Mots clés: Multiferroic hydrothermal method; DRX Transmission; Electron microscopy; Mössbauer spectroscopy; magnetic characterization; Multiferroic hydrothermal method; Multiferroic hydrothermal method; Multiferroic hydrothermal method; Multiferroic hydrothermal method; Multiferroic hydrothermal method; Multiferroic hydrothermal method; Multiferroic hydrothermal method

Domaines: Physique [physics]

Ikbel Mallek Zouari, W. Ben Taazayet, J.-M. Grenèche, Lotfi Bessais, B. Dkhil, et al.. Field-induced spin cycloidal modulation to antiferromagnetic transition and possible flexomagnetic effect in BiFeO3 nanoparticles. Journal of Alloys and Compounds, 2023, 934, pp.167944. ⟨10.1016/j.jallcom.2022.167944⟩. ⟨hal-03975225⟩