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

Fe ions of dose 8 × 10¹⁶ 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 (T_B = 25 K), indicated by zero field cooling and field cooling (ZFC/FC) measurements.