Ferromagnetic behavior above room temperature of Fe-ion-implanted ZnO

Abstract

Zinc-oxide (0001) single crystals with a 0.5 mm thickness were prepared, and then 80 keV Fe ions with a dose of 3 x 10(16) ions/cm(2) were implanted into the ZnO single crystals at 350 degrees C. The implanted samples were post-annealed at 700, 800 and 900 degrees C by rapid thermal annealing in an N-2 atmosphere for 5 min to remove the ion-implantation damage. The structure and the magnetic properties of Fe-ion-implanted ZnO were investigated by using X-ray diffraction and a superconducting quantum interference device magnetometer. The carrier transport properties were measured in the range from 5 K to 300 K. The X-ray diffraction results showed an island peak near 37 degrees C, which was identified as ZnO2. The magnetization curve showed hysteresis loops at 5 K in the samples annealed at 700 and 800 degrees C, showing ferromagnetism. Hysteresis loops were observed at 300 K in the samples annealed at 700 degrees C. The temperature dependence of the magnetization was taken in field cooling (FC) and zero field cooling (ZFC) in the samples annealed at 700 degrees C. The difference magnetization (Delta M) between the FC and the ZFC magnetizations did not converge to a zero value even at 340 K, showing ferromagnetism above room temperature. The magnetoresistance (MR) curve showed negative curvature up to 150 K which could be explained with the delocalized d state of ZnO implanted with Fe ions.