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.