Abstract
We have investigated the relation between local structure, valence and carrier type with magnetism in the Zn-Co-O system. Thin films ranging from wurtzite Zn1−xCoxO (Co:ZnO) to ZnCo2O4 spinel were grown on c-sapphire substrates. On the one hand, the unprecedented doping of x = 0.6 Co in ZnO enables to study the structural and magnetic properties well-above the coalescence limit. On the other hand, the ZnCo2O4 spinel provides a p-type environment. We find a strong correlation between local structure, valence and carrier type throughout the Zn-Co-O system. In contrast to earlier publications neither 60% Co:ZnO nor ZnCo2O4 exhibit any sign of ferromagnetic order despite of the high concentration of magnetic ions and a p-type carrier background. Instead, antiferromagnetic exchange is found to be the predominant magnetic interaction in the Zn-Co-O system.
Highlights
Oxide semiconductors and especially doped ZnO have attracted considerable attention over the last decade because of the variety of possible applications
The relation between local structure, valence and carrier type with the resulting magnetic properties of the Zn-Co-O system from the highly doped wurtzite dilute magnetic semiconductors (DMS) Co:ZnO to the ZnCo2O4 spinel end of the compositional range was never studied before, it would offer the possibility to study the perspectives for both, coalescence and hole-mediated ferromagnetism throughout the entire Zn-Co-O system
A more thorough investigation based on X-ray absorption near edge spectroscopy (XANES) measurements offers the possibility to probe the local structure and valency with element selectivity
Summary
Zn-Co-O system: tuning local received: 17 August 2015 accepted: 21 October 2015 Published: 18 November 2015 structure, valence and carrier type from extremely Co doped ZnO to ZnCo2O4. We have investigated the relation between local structure, valence and carrier type with magnetism in the Zn-Co-O system. Oxide-based dilute magnetic semiconductors (DMS) and especially ZnO doped with transition metal ions like Co (Co:ZnO) have been studied since decades, e.g., Refs. ZnCo2O4 was reported to behave as hole-mediated ferromagnetic semiconductor[17,18] It has even been held responsible for the observed ferromagnetism in some Co:ZnO DMS samples as a potential secondary phase[19]. The relation between local structure, valence and carrier type with the resulting magnetic properties of the Zn-Co-O system from the highly doped wurtzite DMS Co:ZnO to the ZnCo2O4 spinel end of the compositional range was never studied before, it would offer the possibility to study the perspectives for both, coalescence and hole-mediated ferromagnetism throughout the entire Zn-Co-O system. The entire sample series could be grown from one single mixed-oxide target using reactive magnetron sputtering and solely varying the preparation conditions
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