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Following the theoretical predictions of ferromagnetism in Mn-and Co-doped ZnO, several workers reported ferromagnetism in thin films as well as in bulk samples of these materials. While some observe room-temperature ferromagnetism, others find magnetization at low temperatures. Some of the reports, however, cast considerable doubt on the magnetism of Mn-and Co-doped ZnO. In order to conclusively establish the properties of Mn-and Co-doped ZnO, samples with 6 % and 2 % dopant concentrations, have been prepared by the low-temperature decomposition of acetate solid solutions. The samples have been characterized by x-ray diffraction, EDAX and spectroscopic methods to ensure that the dopants are substitutional. All the Mn-and Co-doped ZnO samples (prepared at 400 ºC and 500 ºC) fail to show ferromagnetism. Instead, their magnetic properties are best described by a Curie-Weiss type behavior. It appears unlikely that these materials would be useful for spintronics, unless additional carriers are introduced by some means.

Nanotubes and nanowires of CdSe and CdS have been obtained from solutions containing a surfactant such as Triton 100-X. They have been characterized by x-ray diffraction, electron microscopy, and optical spectroscopy.

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A series of colloidal M x Fe 3−x O 4 (M = Mn, Co, Ni; x = 0−1) nanoparticles with diameters ranging from 6.8 to 11.6 nm was synthesized by hydrothermal reaction in aqueous medium at low temperature (200 °C). Energy-dispersive X-ray microanalysis and inductively coupled plasma spectrometry confirm that the actual elemental compositions agree well with the nominal ones. The structural properties of the obtained nanoparticles were investigated by powder X-ray diffraction, Raman spectroscopy, Mossbauer spectroscopy, X-ray and neutron pair distribution function analysis, and electron microscopy. The results demonstrate that our synthesis technique leads to the formation of chemically uniform single-phase solid solution nanoparticles with cubic spinel structure, confirming intrinsic doping. The local structure of the Fe 3 O 4 NPs is distorted with respect to the cubic inverse-spinel structure, while chemical substitution of Fe by Mn or Ni partially eliminates the local distortions. Magnetic studies showed that, in comparison to nondoped Fe 3 O 4 , the saturation magnetization (M s ) of M x Fe 3−x O 4 (M = Mn, Ni) decreases with increasing dopant concentration, while Co-doped samples showed similar M s . On the other hand, whereas Mn-and Ni-doped nanoparticles exhibit superparamagnetic behavior at room temperature, ferrimagnetism emerges for Co x Fe 3−x O 4 nanoparticles, which can be tuned by the level of Co doping.

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