Synthesis and characterization of novel ferrite–piezoelectric multiferroic core–shell-type structure

Hybrid ferromagnetic/piezoelectric core–shell nanoparticles and ceramics have potential for a wide range of applications due to their tunability, electronic and magnetic properties. In this study, we designed a core–shell-type nanostructure of composition CoFe 2 O 4 /BNT-BT 0.08 , where BNT-BT 0.08 is the abbreviation of bismuth, sodium titanate ( Bi 0.5 Na 0.5 TiO 3 , BNT ) doped with 8 mol% barium titanate (BaTiO 3 , BT). This multiferroic composite was prepared by covering CoFe 2 O 4 nanoparticles with a shell of BNT-BT 0.08 using the sol–gel technique. Scanning and transmission electron microscopy confirmed formation of a core–shell structure. The results of microstructure, dielectric, piezoelectric and magnetic investigations demonstrated that this heterostructure shows simultaneously electrical and magnetic behavior, at room temperature. XRD pattern of core–shell composite CoFe 2 O 4 /BNT-BT 0.08 powder reveals only cubic CoFe 2 O 4 and rhombohedral Bi 0.5 Na 0.5 TiO 3 phases. CoFe 2 O 4 /BNT-BT 0.08 core–shell nanostructure sample shows high values of permittivity ( ε ≥ 600) together with high dielectric losses (tan δ ≥ 1) in the low-frequency range ( ν ≤ 10 4 Hz). PFM and polarization hysteresis indicated a ferroelectric domains structure and remnant polarization of ~ 2.6 µC/cm 2 for the ceramics pellets samples of CoFe 2 O 4 /BNT-BT 0.08 . The present study reveals the possibility of coating nanoparticles onto nanometer-sized core particles, using controlled sol–gel process, in order to prepare multifunctional core–shell composites for piezoelectric and magnetoelectronic sensors.