Among the various approaches to grow semiconducting oxide nanowires, the thermal oxidation procedure is considered a simple, efficient, and fast method that allows the synthesis of micro and nanostructured arrangements with controlled size and morphology. In the work reported in this paper, long ZnO nanowires were synthesized on the surface of oxidized high-purity Zn foils by heating in air at different rates and temperatures. The size and morphology investigated by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) for a sample heated at 620 °C with heating rate of 20 °C/min reveal the growth of long ZnO nanowires with length of ∼50 μm and average diameter of 74 nm grown along the ⟨112̅ 0⟩ direction with high population density. Results with different heating rates indicates that this parameter is determinant in tuning the size, morphology, and population density of nanowires. X-ray diffraction (XRD) shows patterns for both ZnO and metallic Zn with preferential orientation, whereas perturbed angular correlation (PAC) measurements using 111 In( 111 Cd) probe nuclei indicate that probe nuclei occupy only Zn sites in the preferential oriented metallic zinc. However, for samples submitted to high-temperature heating (820 and 1000 °C), XRD yields only the ZnO pattern and, amazingly, PAC continues showing probe nuclei only at metallic Zn sites indicating the presence of thin regions of highly oriented Zn trapped between grains of ZnO. Moreover, this strong preference of indium atoms (of parent radioactive 111 In) here revealed helps to understand the oxidation mechanism and the growth of the nanowires.

The magnetic behavior of Gd2O3 nanoparticles, produced by thermal decomposition method and subsequently annealed at different temperatures, was investigated by magnetization measurements and, at an atomic level, by perturbed γ − γ angular correlation (PAC) spectroscopy measuring hyperfine interactions at 111In(111Cd) probe nuclei. Nanoparticle structure, size and shape were characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). Magnetization measurements were carried out to characterize the paramagnetic behavior of the samples. XRD results show that all samples crystallize in the cubic-C form of the bixbyite structure with space group Ia3. TEM images showed that particles annealed at 873 K present particles with highly homogeneous sizes in the range from 5 nm to 10 nm and those annealed at 1273 K show particles with quite different sizes from 5 nm to 100 nm, with a wide size distribution. PAC and magnetization results show that samples annealed at 873 and 1273 K are paramagnetic. Magnetization measurements show no indication of blocking temperatures for all samples down to 2 K and the presence of antiferromagnetic correlations.

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We herein report a comprehensive investigation on the magnetic, structural, and electric properties of CoO nanoparticles with different sizes by local inspection through hyperfine interactions measured in a wide range of temperatures (10–670 K) by using radioactive $$^{111}$$ 111 In($$^{111}$$ 111 Cd) tracers with the perturbed angular correlations technique. Small cobalt oxide nanoparticles with the characteristic size of 6.5 nm have been prepared by the wet chemical route that turned out to be essential to incorporate radioactivity tracers during nucleation and growth of the particles. Nanocrystalline samples with 22.1 nm size were obtained by thermal treatments under low pressure of helium at 670 K. The hyperfine data were correlated with X-ray diffraction, ZFC–FC magnetic measurements, and transmission electron microscopy to describe the structure, magnetic properties, size, and shape of samples. An analysis of the temperature evolution of hyperfine parameters revealed that the structural distortion and the magnetic disorder in the core and on the surface layer play an important role in the magnetic behavior of CoO nanoparticles.