Preferentially Oriented Nanometer-Sized CoFe₂O₄Mesocrystals Embedded in the BiFeO₃Matrix for Opto-Magnetic Device Applications

CoFe2O4 (CFO) mesocrystals were synthesized in the form of collectively connected nanosized grains with specific crystallographic orientations. Such CFO mesocrystals were found to exhibit distinctive magnetic and optical properties substantially deviating from those observed in conventional CFO single crystals or in a system composed of randomly distributed nanocrystals. In this study, the magnetic and optical properties of CFO mesocrystals having the geometry of rectangular and triangular-shaped islands were extensively investigated. The magnetic strength and anisotropy behavior of rectangular CFO mesocrystals are larger than the triangular ones embedded in the BiFeO3 (BFO) matrix. The result indicates that the orientation of CFO mesocrystals and the magnetic exchange interactions at the CFO-BFO vertical interfaces are important to tune the magnetic properties of CFO mesocrystals. The strain states among the two constituent phases and the substrate also exhibited significant variations in the oxygen vacancy concentration, which in turn plays a determinate role in the optical behavior of the samples. The CFO mesocrystals embedded in rhombohedrally structured BFO matrix having Fe3+/Fe2+ ratio of 1.71 had a slightly smaller band gap than those embedded in a tetragonally structured BFO matrix with Fe3+/Fe2+ ratio of 2.52. The present study demonstrates an intriguing pathway for exploring new opportunities based on a functional CFO mesocrystal-embedded system for practical applications in opto-magnetic-related devices such as magneto-photovoltaics, memory devices, and sensors.