Abstract
Ferromagnetic–ferroelectric nanocomposites are of interest for realizing strong strain-mediated coupling between electric and magnetic subsystems due to a high surface area-to-volume ratio. This report is on the synthesis of nickel ferrite (NFO)–barium titanate (BTO) core–shell nanofibers, magnetic field assisted assembly into superstructures, and studies on magneto-electric (ME) interactions. Electrospinning techniques were used to prepare coaxial fibers of 0.5–1.5 micron in diameter. The core–shell structure of annealed fibers was confirmed by electron microscopy and scanning probe microscopy. The fibers were assembled into discs and films in a uniform magnetic field or in a field gradient. Studies on ME coupling in the assembled films and discs were done by magnetic field (H)-induced polarization, magneto–dielectric effects at low frequencies and at 16–24 GHz, and low-frequency ME voltage coefficients (MEVC). We measured ~2–7% change in remnant polarization and in the permittivity for H = 7 kOe, and a MEVC of 0.4 mV/cm Oe at 30 Hz. A model has been developed for low-frequency ME effects in an assembly of fibers and takes into account dipole–dipole interactions between the fibers and fiber discontinuity. Theoretical estimates for the low-frequency MEVC have been compared with the data. These results indicate strong ME coupling in superstructures of the core–shell fibers.
Highlights
Materials with simultaneous long-range ordering of magnetic and electric dipoles are multiferroic.Single-phase multiferroics that show evidence for coupling between the magnetic and electric subsystems were investigated extensively in the past [1,2,3,4,5]
This work is on the synthesis of nanowires of nickel ferrite (NiFe2 O4, NFO) and barium titanate (BaTiO3, BTO) by electrospinning, as well as assembling into films and discs in a magnetic field, and measurements of ME interactions
The fibers annealed at high temperatures were imaged by scanning electron microscopy (SEM)
Summary
Materials with simultaneous long-range ordering of magnetic and electric dipoles are multiferroic. The ME coupling, in this case, arises due to magnetostriction in the ferromagnetic phase and piezoelectric effect in the ferroelectric phase, leading to an electrical response in an applied magnetic field H or a change in magnetization or anisotropy field in an electric field E Such composites made by co-sintering ferrites and barium titanate were first studied in the 1970s and the ME coupling was found to be rather weak due to leakage currents [13,14]. This work is on the synthesis of nanowires of nickel ferrite (NiFe2 O4 , NFO) and barium titanate (BaTiO3 , BTO) by electrospinning, as well as assembling into films and discs in a magnetic field, and measurements of ME interactions. Structural and ferroic order parameter characterization, assembly of fibers in magnetic fields, results of ME coupling, and our theory are discussed
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