Multiferroic Core-Shell Nanofibers, Assembly in a Magnetic field and Studies on MagnetoElectric Interactions

摘要

Ferromagnetic-ferroelectric nanocomposites are of interest for realizingstrong strain mediated coupling between electric and magnetic subsystems due tohigh surface area-to-volume ratio. This report is on the synthesis of nickelferrite (NFO) -barium titanate (BTO) core-shell nano-fibers, magnetic fieldassisted assembly into superstructures, and studies on magneto-electric (ME)interactions. Electrospinning techniques were used to prepare coaxial fibers of0.5-1.5 micron in diameter. The core-shell structure of annealed fibers wasconfirmed by electron microscopy and scanning probe microscopy. The fibers wereassembled into discs and films in a uniform magnetic field or a field gradient.Studies on ME coupling in the assembled films and discs were done by magneticfield H induced polarization, magneto-dielectric effects at low frequencies andat 16-24 GHz, and low frequency ME voltage coefficients (MEVC). We measured 2~2-7% change in remnant polarization and in the permittivity for H = 7 kOe, anda MEVC of 0.4 mV/cm Oe at 30 Hz. A model has been developed for low-frequencyME effects in an assembly of fibers and takes into account dipole-dipoleinteractions between the fibers and fiber discontinuity. Theoretical estimatesfor the low-frequency MEVC have been compared with the data. These resultsindicate strong ME coupling in superstructures of the core-shell fibers.