Strain Mediated Magneto-Electric Effects in coaxial nanofibers of Y or W type hexagonal ferrites and ferroelectric PZT or Barium Titanate*

This work is on the synthesis of coaxial nanofibers of Y- or W-type hexagonal ferrites and barium titanate (BTO) or lead zirconate titanate (PZT) by electrospinning, assembly of the fibers into films in a magnetic field and measurements of strengths of magnetoelectric (ME) interactions. Electrospinning was carried out in electric fields of ~ 2 kV/cm by dispensing sol-gels of the ferrites and ferroelectrics through a dual chamber needle. Core-shell fibers with an average diameter of 0.5 to 1.5 micron were prepared. Fibers annealed at 700-900 C were found to be free of impurity phases by x-ray diffraction. The core-shell structure was confirmed by electron- and scanning probe microscopy. The nanofibers showed ferroelectric and ferromagnetic order parameters expected for bulk materials. ME coupling strength was measured for films assembled in magnetic fields. Fibers with PZT and W-type hexaferrites showed a higher ME voltage coefficient (MEVC) than for PZT-Y-type ferrites with a maximum value of 20 mV/cm Oe. Films with Y-type ferrite and BTO showed a maximum MEVC of 16.4 mV/cm Oe. The hexaferrite-ferroelectric coaxial nanofibers are of interest for use as miniature sensors of magnetic fields.