Authors: D. Milivojević, Jovan Blanuša, V. Spasojević, V. Kusigerski, B. Babić-Stojić
Abstract: Zn-Mn-O semiconductor crystallites with nominal manganese concentration x = 0.01,
0.02, 0.04 and 0.10 were synthesized by a solid state reaction route using oxalate precursors.
Thermal treatment procedure was carried out in air at different temperatures in the range 400 -
900°C. The samples were investigated by X-ray diffraction, magnetization measurements and
electron paramagnetic resonance. X-ray analysis reveals that dominant crystal phase in the
Zn-Mn-O system corresponds to the wurtzite structure of ZnO. Room temperature ferromagnetism
is observed in the Zn-Mn-O samples with lower manganese concentration, x ≤ 0.04, thermally
treated at low temperature (500°C). Saturation magnetization in the sample with x = 0.01 is found
to be 0.05 μB/Mn. The ferromagnetic phase seems to be developed by Zn diffusion into Mn-oxide
grains.
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Authors: R.K. Singhal, M.S. Dhawan, S.K. Gaur, Elisa Saitovitch
Abstract: ZnO semiconductor doped with a few per cent of some transition metal ions can exhibit above room temperature ferromagnetism, transforming it into a very promising candidate for future spin-electronic applications. In the present article we have compared the electronic structure of two polycrystalline ZnMnO pellets doped with diluted Mn concentration (2% and 4%), carefully characterized by SQUID and XRD, including Rietveld refinement. The characterization measurements established that the samples have the ZnO lattice with ZnS type Wurtzite hexagonal symmetry and no detectable impurities. The samples exhibit distinctly different magnetic properties. The 2% sample displayed a clear FM ordering at 300 K while the 4% sample did not show any ordering down to 5K. The electronic structure of these two samples has been investigated using Mn L23 x-ray absorption spectroscopy, Zn 2p and 3p, Mn 3p and O 1s x-ray photoemission spectroscopy. Our aim was to find out how the changes in the electronic structure can correlate to the observed magnetic properties in such diluted magnetic semiconductor materials. The results show that most of the Mn ions of the ferromagnetic sample are in the divalent state. For the higher Mn percent nonmagnetic sample, a larger contribution of higher oxidation Mn states are dominant and the oxygen content also increases. The two factors can be correlated to the suppressed ferromagnetism, though it is hard to pinpoint that which of these two weighs more in the suppression mechanism.
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Authors: Yun Kai Qi, Jian Jun Gu, Li Hu Liu, Hui Yuan Sun
Abstract: Al doped ZnO films have been prepared by dc magnetron sputtering. These films were annealed in different atmosphere and temperature. The crystal structures were analyzed by x-ray diffraction (XRD), and the magnetic properties were measured by a Physical Properties Measurement System (PPMS) with the magnetic field paralleled to the films plane. The results show the microstructure and magnetic properties were influenced by annealing atmosphere. Compared to the films annealed in vacuum, the films annealed in air shows obvious room temperature ferromagnetism, the magnetic moment increases about an order of magnitude. The room temperature ferromagnetism may be associated with a charge transfer between Al and Zn and the variational position of Al in ZnO films in different annealing ambience.
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