Electron-Spin-Resonance Study of Polycrystalline Zn1−x Cr x O Ceramics
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The structural and magnetic properties of polycrystalline ceramics of Zn1−x Cr x O (x=0.01–0.10) annealed at 900 and 1200 °C were systematically investigated by means of X-ray diffractometer, electron spin resonance (ESR) spectroscopy, and a superconducting quantum interference device magnetometer. A coexistence of two structural phases of wurtzite-ZnO and spinel-ZnCr2O4 was found even in the samples with the lowest Cr-doping concentration of 1 at.%. Our experimental results have indicated that Cr ions are incorporated into the Zn site of the ZnO host lattice, and act as paramagnetic centers. Higher annealing temperature enhances the formation tendency of ZnCr2O4, and the proportion of Cr2+ relative to Cr3+ in ZnO. This results in the broadening of ESR spectral line. Dipole exchange interactions due to Cr3+–Cr3+, Cr3+–Cr2+, and Cr2+–Cr2+ pairs are assigned to be responsible for the ESR signals and paramagnetic behavior of Zn1−x Cr x O samples.
KeywordsCr-doped ZnO Dilute magnetic semiconductors Electron spin resonance X-ray diffraction
This research was supported by the Converging Research Center Program funded by the Ministry of Education, Science and Technology (2012K001431), South Korea.