Room temperature ferromagnetism with high magnetic moment and optical properties of Co doped ZnO nanorods synthesized by a solvothermal route

Zn1−xCoxO (x = 0, 0.05, and 0.07) nanorods (NRs) exhibiting ferromagnetism above room temperature and with high magnetic moment have been synthesized by a solvothermal route. XRD, FESEM, TEM, EDS and XPS measurements reveal the growth of single phase wurtzite structure Zn1−xCoxO NRs with the successful incorporation of Co ions inside the ZnO matrix. TEM micrograph reveals clearly the formation of long ZnO NRs with diameter of 50-90 nm and length of 0.3-0.6 μm. High resolution TEM lattice images and the electron diffraction patterns show that all the NRs are single crystalline. Room temperature magnetic measurements exhibit ferromagnetic behavior with high magnetic moment of 1.83 emu/g for 2 T field, coercivity of 53 G. Temperature dependent magnetization measurement shows a Curie temperature of the order of 398 K. Photoluminescence (PL) spectra exhibit near band edge UV emission and defect related visible emission, which is expected to play a significant role in the FM ordering. PL and UV-VIS spectra reveal slight modification of band edge due to doping effect. Systemic structural, magnetic, and optical studies reveal that both the nature of the defects as well as Co2+ ions are significant ingredients to attain high moment as well as high ordering temperature in the 1-dimensional ZnO NRs. Magnetic interaction is quantitatively analyzed and explained using a bound magnetic polaron model and expected to arise from the intrinsic exchange interaction of Co ions and VZn, Oi related defects. These findings provides a better insight into the underlying mechanisms of high temperature ferromagnetism in Zn1−xCoxO NRs.