Vacancy induced room temperature ferromagnetism in Cu-doped ZnO nanofibers

Abstract

We fabricated ZnO nanofibers by electrospinning a solution containing ZnO precursor and calcination at 600 °C. The electrospun ZnO nanofibers were doped in two methods: adding Cu salt in the sol-gel precursor before electrospinning and thermally diffusing Cu atoms into the pure ZnO nanofibers. Magnetic characterizations show that the ZnO nanofibers doped by adding Cu salt in the sol-gel precursor before electrospinning are paramagnetic while those doped by thermal in-diffusion exhibit ferromagnetism at room-temperature. X-ray photoelectron and photoluminescence spectra demonstrate that the ferromagnetism observed at room-temperature is an intrinsic property of Cu-doped ZnO nanofibers fabricated by thermal in-diffusion, and does not originate from any secondary phase. A comparative study of Cu-doped ZnO nanofibers fabricated by two distinct methods indicates that Cu doping by diffusion does not induce phase segregation but leads high level of oxygen vacancies and the room temperature ferromagnetism of Cu-doped ZnO nanofibers fabricated by thermal in-diffusion is associated with the oxygen vacancies.