Ferromagnetism in Fe-doped ZnO Nanocrystals: Experimental and Theoretical investigations

TL;DR

This study combines experimental synthesis and characterization with theoretical calculations to explore ferromagnetism in Fe-doped ZnO nanocrystals, revealing high transition temperatures and the role of defects and hole doping in magnetic behavior.

Contribution

It provides new insights into the origin of ferromagnetism in Fe-doped ZnO, emphasizing the impact of vacancies and hole doping through combined experimental and ab-initio approaches.

Findings

Ferromagnetic transition temperature > 450 K

Presence of Fe in Fe2+ and Fe3+ states confirmed

Hole doping via Zn vacancies stabilizes ferromagnetism

Abstract

Fe-doped ZnO nanocrystals are successfully synthesized and structurally characterized by using x-ray diffraction and transmission electron microscopy. Magnetization measurements on the same system reveal a ferromagnetic to paramagnetic transition temperature > 450 K with a low-temperature transition from ferromagnetic to spin-glass state due to canting of the disordered surface spins in the nanoparticle system. Local magnetic probes like EPR and Mossbauer indicate the presence of Fe in both valence states Fe2+ and Fe3+. We argue that the presence of Fe3+ is due to the possible hole doping in the system by cation (Zn) vacancies. In a successive ab-initio electronic structure calculation, the effects of defects (e.g. O- and Zn-vacancy) on the nature and origin of ferromagnetism are investigated for Fe-doped ZnO system. Electronic structure calculations suggest hole doping (Zn-vacancy) to be more effective to stabilize ferromagnetism in Fe doped ZnO and our results are consistent with the experimental signature of hole doping in the ferromagnetic Fe doped ZnO samples.