Strong room temperature ferromagnetism in chemically precipitated ZnO:Co²⁺:Bi³⁺ nanocrystals for DMS applications

Abstract

Well crystalline Co-Bi co-doped ZnO nanostructures with various concentration of Bi were synthesized by simple chemical precipitation technique using metal nitrate precursors. The structural and magnetic properties of the samples calcined at 300 °C for 6 h has been studied comprehensively. X-ray diffraction patterns of the pure and Co-with Bi doped samples have shown the well crystalline diffraction peaks corresponds to the characteristic wurtzite ZnO crystal structure. Aggregated nano particles have emerged with flower like morphology and it can be seen from the scanning electron microscopy and transmission electron microscopy. The average particle diameter was estimated and found to be 25–35 nm. Tunable optical band gap related to an additional electron state created by dopant was observed from the UV–Visible spectra. Typical PL emission in the UV, visible and continuous deep level emission further demonstrates that the potential application of the material in optoelectronics. Excellent ferromagnetic features of the material at room temperature reveal the additional carrier induced exchange interaction could enhance the ferromagnetism in co-doped ZnO nanostructure. The addition of Bi at 3⁺ states can act as donor within the semiconductor which provides the additional electron charge carrier that could involve directly to the exchange interaction effectively at certain limit and enhances the ferromagnetism. At higher doping concentration the formation of diamagnetic Bi₂O₃ secondary phase have contributed to change the ferromagnetic behaviour of the sample. From this study it is suggested that this kind of combined ferromagnetism and excellent optical tunability of the Bi co-doped ZnO:Co system will be the potential material for future magneto-opto-electronic devices.