Evidence of various stabilizing mechanisms in ferromagnetic Co doped ZnO nanocrystals

In spite of the extensive investigations on Co-doped ZnO, existence as well as origin of ferromagnetism remains controversial. Role of charge carriers and defects on the ferromagnetic ordering of Al, Co-codoped ZnO nanocrystals (NCs) having size as small as 5.5 nm is evaluated on the basis of optica...

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Bibliographic Details
Published in:Journal of alloys and compounds 2017-12, Vol.726, p.947-954
Main Authors: Doke, Swapnil, Sonawane, Kiran, Banerjee, Alok, Mahamuni, Shailaja
Format: Article
Language:English
Subjects:
Absorption spectra
Alloys
Current carriers
DMS
Electron paramagnetic resonance
Electron spin
Exchange interactions
Ferromagnetic
Ferromagnetism
Magnetic saturation
Magnetism
Nanocrystals
Raman
Spin resonance
Zinc oxide
ZnO
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Summary:In spite of the extensive investigations on Co-doped ZnO, existence as well as origin of ferromagnetism remains controversial. Role of charge carriers and defects on the ferromagnetic ordering of Al, Co-codoped ZnO nanocrystals (NCs) having size as small as 5.5 nm is evaluated on the basis of optical spectroscopy, electron spin resonance and Raman spectroscopy. Al, Co-codoped ZnO NCs reveal improved saturation magnetization in a subtle way. Concomitant increase in the charge carriers is vivid from the optical absorption spectra of colloidal codoped NCs. The doping level is maintained low enough so that NCs are free of any secondary or impurity phase. Shape of the M(T) curves is analyzed to elucidate exchange interaction in doped ZnO NCs. The present experimental work indicates that the multiple mechanisms are responsible for stabilizing the ferromagnetic ordering in Co-doped ZnO NCs; thereby controversial reports are published in the literature. •Ferromagnetism in nanocrystals (NCs) has very different origin than bulk.•NCs are ensured to be free of any secondary phase.•Al incorporation in ZnO NCs assists ferromagnetic ordering.•Doping n-type impurities in small NCs and defects induce ferromagnetism.•Ferromagnetic ordering in NCs is stabilized by BMP and RKKY interactions.
ISSN:0925-8388
1873-4669
DOI:10.1016/j.jallcom.2017.08.034