Synthesis, structural and magnetic characterization of highly ordered single crystalline BiFeO3 nanotubes

In this work, we report on the fabrication of highly ordered single crystalline BiFeO3 (BFO) nanotubes by a sol–gel technique using two-step anodic aluminum oxide (AAO) as template. We prepared BFO nanotubes with dimensions of 65 nm in diameter and 3 μm in length, as confirmed by scanning electron microscopy (SEM) measurements. The obtained single crystalline nanotubes present the expected pure phase (BiFeO3) as confirmed by energy-dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). In addition to the antiferromagnetic behavior, the magnetization curves of the BFO nanotubes also present a ferromagnetic response, which holds from 2 to 300 K. This desirable behavior is associated to the break of the antiferromagnetic helical spin ordering of the BFO nanotubes. Besides the magnetocrystalline anisotropy, the large length-to-diameter ratio induced an uniaxial shape anisotropy, attested by the applied magnetic field angle measurements.

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► Highly ordered BiFeO3 nanotubes with 65 nm of diameter and 3 μm of length.
► Its morphology is smooth revealing, by TEM, a single crystalline structure.
► Suppression of the antiferromagnetic helical order giving rise to ferromagnetism.
► The large length-to-diameter ratio of the BiFeO3 nanotubes induced an uniaxial shape anisotropy which is added to the magnetocrystalline anisotropy.