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Proceedings ArticleDOI

Absence of Ferromagnetism in Mn Doped ZnO

05 Jul 2011-Vol. 1347, Iss: 1, pp 206-209

Abstract2 and 4 at% Mn doped ZnO samples were synthesized by sol‐gel technique. The structural, compositional and magnetic properties were investigated. The 4 at% Mn doped sample contains secondary phase of ZnMnO3. The compositions of the samples are close to perfection. Crystallite size decreases with increase in doping. Both samples indicate absence of ferromagnetism. Strong presence of antiferromagnetism was found and it falls with increasing Mn doping. Simultaneously paramagnetic fraction of spin increases. more

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Abstract: The structural, optical and magnetic properties of Mn doped ZnO nanocrystalline particles, Zn1-xMnxO, with different percentages of Mn content have been studied. XRD and XPS measurements showed that all samples with Mn doping up to x = 0.1 possess typical wurtzite structure and have no other impurity phases. The incorporation of Mn ions into the ZnO lattice was also confirmed by FTIR and UV–Vis. spectroscopy results. Both XRD and SEM results indicated a slight decrease in the grain size with increasing the Mn doping level. The XPS results indicated an increase in the oxygen vacancies concentration with increasing the Mn doping level. The magnetization measurements revealed a weak ferromagnetic behavior at room temperature and a clear ferromagnetic behavior with relatively large coercive fields at low temperature. The ferromagnetic order is improved by increasing the Mn doping. In addition, we observed an increase in the concentration of oxygen vacancies, which is also induced by increasing the Mn doping level. A ferromagnetic coupling of the local moment of Mn dopants through the sp-d exchange interaction and oxygen vacancies, in addition to different magnetic contributions due to different forms of Mn ions that coexist in the Mn doped nanoparticles were presented in order to interpret the observed magnetic behavior. We observed a clear red shift in the direct band gap and an increase in the coercive field and saturation magnetization values with increasing the Mn doping level.

55 citations

Journal ArticleDOI
Abstract: X-ray diffraction, electron paramagnetic resonance, Fourier transform infrared spectroscopy and scanning electron microscopy were used to study the defect formation and reaction processes in a ZnO + 1%Gd 2 O 3 powder mixture during its mechanical and laser processing. Mechanical treatment of the ZnO + 1%Gd 2 O 3 powder mixture leads to a grinding of initial ZnO particles and formation of three types of superficial paramagnetic donor defect centers. The rise of the sample temperature with increasing processing time promotes a successive annealing of ZnO defects with small activation energies and of superficial defects in Gd 2 O 3 . The formation of a ZnO:Gd 3+ solid solution in the used mechanical processing regimes has not been observed. Laser surface melting of the ZnO + 1%Gd 2 O 3 pellets provokes formation of a surface layer exhibiting a texture. The crystallization directions in the superficial layers of different specimens have a random character. In the superficial layers and deep sub-surface layers, processes of solid-state interactions (formation of an inhomogeneous ZnO:Gd 3+ solid solution) take place. The surplus charges of the Gd 3+ ions are compensated by the formation of Zn vacancies or interstitial oxygen ions which in the laser-surface-melted layers are located closer to the Gd 3+ ions than in the case of single-crystalline samples.

2 citations