Effect of cobalt substitution on microstructure and magnetic properties in ZnO nanoparticles

Abstract

: Ferromagentic semiconductors have been actively pursued because of their potential as spin polarized carrier sources and easy integration into semiconductor technology. One such material, ZnO has been shown to be a potential Diluted Magnetic Semiconductor (DMS). The appearance of ferromagnetism, however, is found to be sensitive to the processing conditions. We report synthesis of ZnO nanoparticles of size ~20 nm by a simple co-precipitation technique using metal nitrates and NaOH as precipitant. The particles are selforganised and reveal single crystalline behaviour in electron diffraction pattern. Incorporation of Co in ZnO matrix leads not only to the reduction in crystallite size but also to the modification of the structure. At 5% Co, the particles are highly textured. The particles also aggregate and the aggregated mass have nearly rectangular shape as seen through TEM. Increasing Co to 10%, results into further reduction of particle size and the particles self organize in a line, which looks like nanofibers. This alignment of particles increases by increasing the Co content further. This type of growth of nanofibers above Co ≥ 10% is well correlated with the anisotropic peak broadening observed in the XRD spectra. In addition, Co substitute Zn site up to 20% without showing any extra phase in XRD spectra as compared to 7 to 10% in case of bulk. Transport and magnetic studies indicate that conductivity increases with increasing Co content, but carrier mediated ferromagnetism is absent down to 10 K.

Combustion synthesis of Co-doped zinc oxide nanoparticles using mixture of citric acid–glycine fuels

“…Previous work has demonstrated that for solid state reaction a complete solid solution of Co:ZnO can be achieved by addition of 0-20 wt% of Co 3 O 4 [11]. Since low amounts of cobalt (less than 5%) are not detectable by XRD technique, 10 wt% Co was used to insure complete formation of solid solution.…”

“…Co doped with ZnO has been synthesized via sol-gel [7], hydrothermal [8], wet chemical [9,10] and precipitation methods [11]. However, Co doped ZnO nanoparticles could be prepared by fast, simple and inexpensive solution combustion method [12].…”

Hydrothermal synthesis of Co-doped ZnO flakes with room temperature ferromagnetism

“…However, experimental observations of magnetism of the Co-doped ZnO synthesized by different methods have been controversial for both thin films and bulk samples. A number of groups observed no ferromagnetism in Zn 1−x Co x O [4][5][6], while Kalyana Lakshmi et al [7] and Maensiri et al [8] reported ferromagnetism in Co-doped ZnO powders. Kittilstved et al [9] and Rubi et al [10] demonstrated that ferromagnetism of n-type Zn 1−x Co x O thin films and powders could be switched on or off by chemical manipulation using nitrogen or oxygen, respectively.…”

Effect of Co Doping on Structural and Optical Properties of Zinc Oxide Nanoparticles Synthesized by Sol-Gel Method

“…From micrographs, it is clear that the cauliflower like ZnO comprising of nanoclusters observed on the surface of the ZnO Nanoparticles and almost spherical shape morphology in doped ZnO. The morphological observation of SEM results indicates particles with less aggregation can be obtained from this method [18].…”