Peculiarities of the temperature dependence of electron spin resonance and Raman studies of Zn1-xNixO/NiO two-phase nanocomposites

A meticulous investigation of electron-spin-resonance (ESR) and Raman spectroscopy of the two-phase nanocomposites of Zn1-xNixO/NiO is reported. The temperature variation of X-band ESR parameters viz., resonance field H-R(T) and line-width Delta H-PP(T) follows the power-law variation (delta H-R = (Delta H-PP)(n)) of Nagata and Ishihara model, which was used to understand the orientation of statistical ensemble of particles with respect to a given direction of the anisotropy axis. This analysis yields the exponent "n" similar or equal to 2.13 and 2.85 for the composite system Zn1-xNixO/NiO and pure NiO suggesting the presence of partial and randomly oriented ellipsoidal nanocrystallites, respectively. The Raikher and Stepanov model has been employed to probe the role of amorphous Ni3+ clusters on the observed ESR spectra. Interestingly, after Ni substitution, a new zone boundary phonon mode was noticed at 129 cm(-1) for all the samples, which is usually forbidden in the first-order Raman scattering for wurtzite ZnO. In addition to the 2M magnon mode, two extra modes appear at 558 and 900 cm(-1) due to the increased volume fraction of NiO within the Zn1-xNixO matrix. A systematic correlation of the above results with a comparative analysis of their bulk counterpart has been presented. (C) 2016 AIP Publishing LLC.