Magneto-Electric Effects in Core-Shell Nanofibers of Nickel Zinc Ferrite and PZT

The nature of mechanical strain mediated magneto-electric (ME) interactions is investigated in coaxial nanofibers of nickel zinc ferrite and PZT synthesized by electrospinning. Fibers of core diameter 100-200 nm and shell thickness of 100-250 nm with (1-x) Ni xZn Fe2O4 (x = 0.5-0.9) (NZFO) and PZT were made from sols of the ferrite and PZT. For comparison of ME properties, we also synthesized composite fibers with ferrite and PZT by mixing the two sols. Fibers annealed at 700-900 C were found to be free of impurity phases and electron and scanning probe microscopy revealed core-shell structure for the coaxial fibers. Ferroic order parameters for the core-shell and composite fibers were an order of magnitude smaller than for bulk materials. The strength of ME interactions were measured in disks of fibers by magnetic field H induced change in polarization P and by low-frequency ME voltage coefficient (MEVC). The fractional change in P for H=7 kOe in core-shell fibers ranged from 3% to 82% with disks of Ni-Zn ferrite with x=0.3 showing the maximum value and were much higher than for composite fibers. The maximum MEVC for core-shell fibers was 17 mV/cm Oe and was an order of magnitude higher than for composite fibers. The coaxial fibers are of importance for use as magnetic sensors and in energy harvesting applications.