Raman scattering studies in dilute magnetic semiconductorZn1−xCoxO

Abstract

Raman spectra of ZnO and Co substituted ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{O}$ (ZCO) were carried out using the Raman microprobe system with an ${\mathrm{Ar}}^{+}$ ion laser source of $514.5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ 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 $(1.2{\ensuremath{\mu}}_{B}∕\mathrm{Co})$ for 10% Co substitution, which decreased with at further increase in Co concentrations. The intensities of ${E}_{1}(\mathrm{LO})$ at $584\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ and multiphonon modes at $540\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ 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.