Nonlinear magnetic response of nanostructured BiFeO3

Reference Presenter Authors
08-027 Gustavo Sanguino Dias Volnistem, E.A.(Maringá State University); Dias, G.S.(Maringá State University); Leonardo, J.M.(Maringá State University); Silva, D.M.(Maringá State University); Garcia, D.(Universidade Federal de São Carlos); Eiras, J.A.(Universidade Federal de São Carlos); Santos, I.A.(Maringa State University); Bismuth Ferrite (BiFeO3) is a multiferroic magnetoelectric material with a rhomboedrally distorted perovskite structure (ABO3) and R3c space group that has attracted the attention of the scientific community due to elevated Currie and Nèel temperatures (Tc ~ 370 Coand Tn ~ 830 Co) making BiFeO3 a promising candidate for technological applications. However, the synthesis of single-phased BiFeO3 remains a challenge considering the formation of undesirable phases such as Bi25FeO39 and Bi2Fe4O9 resultant from elevated temperature and longtime applied during the synthesis process. Besides that, regarding the magnetic properties, the antiferromagnetic behavior is widely reported for BiFeO3 at room temperature and generally attributed to the well-known spin cycloid ordering. In this sense, the size effect on the magnetic properties of BiFeO3 became an important issue since unusual magnetic behaviors has being reported for nanoparticles synthesized by wet-chemical routes with size below cycloid period (64 nm). In this study, single-phased BiFeO3 samples were synthesized by high-energy ball milling followed by fast-firing sintering and, subsequently, nanostructured through high-energy ball milling at cryogenic temperature (cryomilling). The cryomilling time and ball size used as grinding medium were correlated to structural, microstructural and magnetic properties of BiFeO3 nanostructured samples. Williamson-Hall analysis reveal crystallite size reduction up to 32 nm and elevated microstrain values (~ 1.1%) after 2.5 h of cryomilling. Furthermore, an unusual nonlinear magnetic behavior was observed at room temperature presenting an increase of magnetic response as the crystallite size decrease, reaching its maximum for crystallite sizes close to half of BiFeO3 cycloid size. In addition, a phenomenological study based on Langevin equation were done to evaluate how linear and nonlinear are correlated to the cryomilling settings.
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