In-situ synthesis of novel Co₂FeO₄ needle-like phases for structural and functional integration

In this study, we proposed a new method to prepare yttrium iron garnet/yttrium iron garnet (YIG/YIG) functional joint via in-situ synthesis of novel Co₂FeO₄ needle-like phases. It is found that the formation of the Co₂FeO₄ needle-like phases was controlled by “two-step heterogeneous nucleation”: (i) CoO nanoparticles acted as the preliminary heterogeneous nucleation particle, reacting with O₂ to form Co₃O₄ phase; (ii) The surface of Co₃O₄ phase acted as the subsequent heterogeneous nucleation interface, atoms stacked along the (220) crystal plane of Co₃O₄ to form Co₂FeO₄ phase. Fe³⁺ diffused into the glass matrix which is rich in O²⁻, participating in the reaction with Co₃O₄ and CoO. The Co₂FeO₄ nuclei grew into needle-like phases along the [001] orientation. The Co₂FeO₄ needle-like phases exhibited favourable mechanical property and magnetism according to the nanoindentation and magnetic force microscopy (MFM) analysis. And the shear strength of YIG/YIG joint reinforced by Co₂FeO₄ needle-like phases could reach 72 MPa. The investigation supplies a new synthetic idea of Co₂FeO₄ magnetic needle-like phases, which has significant application potential for the structural and functional integration in electromagnetic field.