Nanosized superparamagnetic precipitates in cobalt-doped ZnO

摘要: The existence of semiconductors exhibiting long-range ferromagnetic ordering at room temperature still is controversial. One particularly important issue the presence secondary magnetic phases such as clusters, segregations, etc. These are often tedious to detect, leading contradictory interpretations. We show that in our cobalt doped ZnO films grown homoepitaxially on single crystalline substrates magnetism unambiguously stems from metallic nano-inclusions. behavior was investigated by SQUID magnetometry, X-ray circular dichroism, and AC susceptibility measurements. results were correlated a detailed microstructural analysis based high resolution diffraction, transmission electron microscopy, electron-spectroscopic imaging. No evidence for carrier mediated exchange between diluted moments found. In contrast, combined data provide clear observed ferromagnetic-like originates nanometer sized superparamagnetic precipitates.