Control of crystalline characteristics of shell in core-shell magnetoelectric nanoparticles studied using HRTEM and holography

ABSTRACT

Magnetoelectric layered composites can be designed to exhibit the magnetoelectric effect based on transfer of stress from magnetostriction of ferromagnetic layer to the ferroelectric layer. In this study Core-Shell magnetoelectric nanoparticles (CSMEN) have been fabricated by coating BaTiO₃ on CoFe₂O₄ nanoparticles (∼50nm) by molar mass ratio using hydro-thermal method. The control factor in the fabrication process is the use of different shape and morphology of the CoFe₂O₄ core. The crystallinity of the barium titanate (BT) coating changes from single crystalline to polycrystalline nature depending on the BT coating thickness. The BT shell thickness during CSMEN fabrication largely varies with the morphology of the substrate which is the cobalt ferrite nanoparticle. The shape, size and coagulation are the morphological characteristics of cobalt ferrite nanoparticles which plays major role for single crystalline BT coating on it. The bigger the size or the uneven surface morphology/shape of cobalt ferrite nanoparticles, the bigger (polycrystalline) BT shells formation by the same process of fabrication. The process of coating of BT shell on cobalt ferrite nanoparticles is analyzed step by step to accurately measure the maximum thickness of shell to sustain single crystallinity. The maximum size of BT coating prepared by this method to sustain single crystallinity is up to 41.2 nm which is approximately ∼100 unit cells of barium titanate. High resolution transmission electron microscopy (HRTEM), selected area electron diffraction pattern (SAED) and holography have been used in this study to visualize and characterize the integrated morphology of CSMEN.

KEYWORDS:

• Core shell magnetoelectric nanoparticles
• holography
• multiferroics
• HRTEM

Acknowledgments

SB, MD, ASB, and RG acknowledge the support of the National Science Foundation under Grant No. 1002380 and by the Department of Defense under the Grant No. W911NF-12-1-0082. Special thanks to Dr Arturo Ponce for his assistance with STEM and holography experiments.