Bi Fu

Magnetic properties of different CoFe2O4 nanostructures: nanofibers versus nanoparticles

We fabricated CoFe2O4 (CFO) nanofibers (NFs) and nanoparticles (NPs) via electrospinning and the conventional sol–gel process, respectively. Sizes of these nanomaterials can be controlled by adjusting the annealing temperature. Magnetic dynamic behaviour showed differences between them. These differences have been linked to specific size and shape configurations. At room temperature, magnetic properties were size dependent, but the specific shape configuration dominated the magnetic properties at 5 K.

Significant increase of Curie temperature and large piezoelectric coefficient in Ba(Ti0.80Zr0.20)O3-0.5(Ba0.70Ca0.30)TiO3 nanofibers

Ba(Ti0.80Zr0.20)O3-0.5(Ba0.7Ca0.3)TiO3 (abbreviated as BTZ-0.5BCT) is a piezoelectric ceramic with a high piezoelectric coefficient d33 (∼620 pC N−1) and has been regarded as one of the most promising candidates to replace PZT-based materials (200–710 pC N−1). However, its Curie temperature TC is relatively low (93 °C) limiting its application. In this letter, we found a temperature dependent Raman spectrum in BTZ-0.5BCT nanofibers (NFs), demonstrating a diffused tetragonal-to-cubic phase transition at 300 °C. This means that the TC of the NFs is nearly 207 °C higher than that of the normal bulk material. The increased TC is considered to be associated with the size effect of BTZ-0.5BCT nanoceramic subunits and the nanoporous nature of the fiber, resulting in discontinuous physical properties. The variation of the ferro/piezoelectricity over the fiber surface is attributed to the polycrystalline structure. The d33 (173.32 pm V−1) is improved in terms of the decreased Q factor result in an increase in d33 ...

Griffith phase-induced ferromagnetic diffuse phase transition

Abstract A ferromagnetic transition is generally regarded as a diffusionless process, exhibiting a sharp change of magnetic properties with temperature. In this paper, however, we report a ferromagnetic diffuse phase transition (FDPT) induced by Griffiths phase in La1 − xSrxMnO3 (0·06 ≤ x ≤ 0·2). Such a FDPT experiences a broad transition temperature range, resulting in temperature-controlled ferromagnetic cluster owing to the existence of Griffiths phase during the diffusion process. The transition temperature range calculated from M–T curve is as large as 146 K for the FDPT sample. Further analysis suggests that this novel FDPT has the same scenario with that in the ferroelectric relaxor, where the ferroelectric clusters are embedded in the paraelectric matrix.

Substrate clamping effect onto magnetoelectric coupling in multiferroic BaTiO3-CoFe2O4 core-shell nanofibers via coaxial electrospinning

We report large lateral magnetoelectric (ME) coupling coefficients α 31 of and in substrate bonded and free-standing multiferroic BaTiO3-CoFe2O4 (BTO-CFO) core-shell nanofibers (NFs) with and without substrate clamping effect, respectively. The BTO-CFO core-shell NFs were synthesised by a sol-gel coaxial electrospinning technique, and their ME coupling was directly observed by demonstrating the evolution of piezoelectric coefficient (d 33), ferroelectric domain, and phase contrast induced by an external magnetic field. These impressed α 31 coefficients originated from the nanoconfinement of the interphase elastic interaction between the ferromagnetic core fiber and the ferroelectric shell interlayer, as well as the strain transformation at the one-dimensional (1D) fiber boundary. This means that the decreasing substrate clamping effect results in an enhanced ME coupling in multiferroic NFs, which is similar to that of thin films. These findings make people understand the substrate clamping effect and enable nanoscale ME device applications.

Magnetoelectric coupling in multiferroic BaTiO3-CoFe2O4 composite nanofibers via electrospinning

Magnetoelectric (ME) coupling in Pb-based multiferroic composites has been widely investigated due to the excellent piezoelectric property of lead zirconate titanate (PZT). In this letter, we report a strategy to create a hybrid Pb-free ferroelectric and ferromagnetic material and detect its ME coupling at the nanoscale. Hybrid Pb-free multiferroic BaTiO3-CoFe2O4 (BTO-CFO) composite nanofibers (NFs) were generated by sol-gel electrospinning. The perovskite structure of BTO and the spinel structure of CFO nanograins were homogenously distributed in the composite NFs and verified by bright-field transmission electron microscopy observations along the perovskite [111] zone axis. Multiferroicity was confirmed by amplitude-voltage butterfly curves and magnetic hysteresis loops. ME coupling was observed in terms of a singularity on a dM/dT curve at the ferroelectric Curie temperature of BaTiO3. The lateral ME coefficient was investigated by the evolution of the piezoresponse under an external magnetic field of 1000 Oe and was estimated to be . These findings could enable the creation of nanoscale Pb-free multiferroic composite devices.