Synthesis of ZnFe2O4 nanomagnets by Fe-ion implantation into ZnO and post-annealing

Fe ions of dose 8×10^16 cm^-2 are implanted into a ZnO single crystal at 180 keV. Annealing at 1073 K leads to the formation of zinc ferrite （ZnFe2O4）, which is verified by synchrotron radiation X-ray diffraction （SR-XRD） and X-ray photoelectron spectroscopy （XPS）. The crystallographically oriented ZnFe2O4 is formed inside the ZnO with the orientation relationship of ZnFe2O4 （111）//ZnO （0001）. Superconducting quantum interference device （SQUID） measurements show that the as-implanted and post-annealing samples are both ferromagnetic at 5 K. The synthesized ZnFe2O4 is superparamagnetic, with a blocking temperature （TB = 25 K）, indicated by zero field cooling and field cooling （ZFC/FC） measurements.