Defect-induced reversible ferromagnetism in Fe-doped ZnO semiconductor: An electronic structure and magnetization study

Effect of injection of hydrogen ions, followed by their evaporation, has been investigated in the Zn1-xFexO (x = 0.02-0.07) pellets to throw some light on electronic structure and magnetic correlations. The XRD patterns show that x <= 0.05 samples are single phase and the Fe ions incorporate at the Zn2+ sites, while a secondary phase ZnFe2O4 is detected for x >= 0.07. The 2% Fe-doped sample retains a paramagnetic ground state down to 50 K. Likewise, the 5% doped sample also shows paramagnetic state at 300 K but a weak ferromagnetic ordering stems from its cooling (T-c similar to 160K). Strikingly, the 5% doped sample, when annealed in hydrogen atmosphere, showed inducement of room temperature ferromagnetism. More significantly, the hydrogen-induced magnetism disappears upon evaporating the H ions by re-heating the sample. The magnetic ordering and the electronic properties exhibit a close parallelism/interplay. The X-ray photoemission spectroscopy results testify the Fe to be in mixed valent state (>2+) in paramagnetic state, however, the ferromagnetic transition stems only upon Fe3+ reducing to Fe2+, accompanied by emergence of oxygen vacancies as a parallel electronic phenomenon. Origin of H-mediated ferromagnetism is discussed in the framework of cationic vs. anionic vacancies and it is suggested that oxygen vacancies play major role in mediating the coupling. (C) 2010 Elsevier B.V. All rights reserved.