An investigation on structural, optical, and magnetic properties of Zn1-xCoxO nanorods fabricated by electrochemical deposition.

We reported here the structural, optical, and magnetic properties of Zn1-xCoxO nanorods (NRs) with x = 0.00, 0.025, 0.05, and 0.30 wt%. The Zn1-xCoxO NRs samples were fabricated by electrochemical deposition and given the symbols S0, S1, S2, and S3 for x = 0.00, 0.025, 0.05, and 0.30 wt%, respectively. It is found that all NR samples were grown along the (002) plane and have a hexagonal structure. As the Co level increases up to 0.30 wt%, the crystallite size and the texture coefficient are respectively decreased from 57 nm to 0.98 to 25 nm and 0.70. While the diameter of NRs increased from 347 to 1730 nm. Interestingly, the weight% (wt %) of O was increased with increasing Co level. The optical band gap (Eg) was found to be 3.32 eV for the undoped ZnO NRs (S0) and reduced to 2.24 eV with more increase of Co up to 0.30 wt%. At 300 K, the So and S1 exhibit diamagnetic behavior over the field range. For S2, such behavior became weakly ferromagnetic at H ≤ 2000 Oe and diamagnetic at H > 2000 Oe. In contrast, the S3 exhibits strong ferromagnetic behavior of magnetization (M) = 0.14 emu/g at 20 kOe. However, with decreasing temperature to 10 K, the paramagnetic behavior is dominant for all NRs. However, all NRs samples revealed a hysteresis loop After subtracting the paramagnetic and diamagnetic contributions from the M-H curves. The S2 showed the highest value for coercive field of 256 and 263 Oe, as compared to the other NRs (15-65 Oe). Although S3 shows the softest magnetic properties among all samples (with coercive fields of 15-27 Oe), it exhibits the strongest ferromagnetic behavior. The Zfc/Fc measurements show that all the samples are paramagnetic by nature with no sign for blocking temperature of magnetic nanoparticles. Furthermore, the residual magnetization values measured at 300 K (from both FC and ZFC curves) show a general increasing trend with cobalt doping concentration, with measured values of 6.45 × 10⁻⁹, 2.13 × 10⁻⁴, 8.71 × 10⁻⁵, and 6.45 × 10⁻² emu/g for samples S0 through S3, respectively. This work provides new insights into the correlation between electrochemical growth conditions, defect chemistry, and room-temperature ferromagnetism in Co-doped ZnO systems, advancing beyond previous reports through its demonstration of bandgap tuning and robust ferromagnetism in electrochemically grown NRs and temperature-dependent magnetic phase transitions directly correlated with structural parameters.