Raman spectra of ZnO and Co substituted ${\mathrm{Zn}}_{1-x}{\mathrm{Co}}_x\mathrm{O}$ (ZCO) were carried out using the Raman microprobe system with an ${\mathrm{Ar}}^{+}$ ion laser source of $514.5\mathrm{nm}$ wavelength. The shift towards the lower frequency side of the nonpolar $E_2^{\text{low}}$ mode and the broadening due to Co substitution in ZnO were analyzed using the phonon confinement model. The magnetic measurements showed ferromagnetic behavior with the maximum saturation magnetization $(1.2{\mu }_B∕\mathrm{Co})$ for 10% Co substitution, which decreased with at further increase in Co concentrations. The intensities of $E_1\left(\mathrm{LO}\right)$ at $584{\mathrm{cm}}^{-1}$ and multiphonon modes at $540{\mathrm{cm}}^{-1}$ were increased with an increase in Co substitution. The additional Raman modes in ceramic targets of ZCO spectra for higher concentration of Co substitution $(x=15\%–20\%)$ were identified to be due to the spinel $\mathrm{Zn}{\mathrm{Co}}_2{\mathrm{O}}_4$ secondary phase.

• Received 13 February 2006

DOI:https://doi.org/10.1103/PhysRevB.73.245213