29 research outputs found
Magnetic Properties of "As-Prepared" and Chemically Modified Multiwalled Carbon Nanotubes
In this work we have studied the structural and magnetic properties of "as-prepared" multiwalled carbon nanotubes, synthesized by the chemical vapor deposition method, and chemically modified multiwalled carbon nanotubes. Transmission electron microscopy was used to show multiwalled carbon nanotubes structure. The results of systematic magnetic property measurements on multiwalled carbon nanotubes are presented. The static and dynamic magnetic responses, such as the temperature dependence of the linear AC susceptibility and DC magnetization up to 9 T were studied. We have observed significant changes in magnetic AC susceptibility and magnetization for "as-prepared" and chemically modified multiwalled carbon nanotubes samples
Synthesis by Wet Chemical Method and Characterization of Nanocrystalline ZnO Doped with
Nanocrystalline samples of ZnO doped with were synthetized by wet chemical method. The series of ZnO nanosized samples in the wide range of concentration (from 5 wt.% to 95 wt.%) was prepared by precipitation from nitrate solutions using ammonia. The phase composition of the samples was determined using X-ray diffraction measurements. The phases of hexagonal ZnO, and/or rhombohedric , and/or were identified. The mean crystalline size of nanocrystals, determined with the use of Scherrer's formula, varied from 8 to 52 nm. The preliminary micro-Raman spectroscopy measurements were performed. The observed features are typical of Fe doped ZnO nanoparticles. The magnetic measurements revealed the presence of different types of magnetic behavior. For samples with high contents (above 70 wt.%) the ferromagnetic ordering was observed at room temperature. For samples with lower contents we observed the phenomenon of superparamagnetism above the blocking temperature
Nanocrystalline ZnO Doped with FeO - Magnetic and Structural Properties
We have studied the magnetic properties of ZnO nanocrystals doped with FeO in the magnetic dopant range from 5 to 70 wt%. The nanocrystals were synthesized by wet chemical method. The detailed structural characterization was performed by means of X-ray diffraction and micro-Raman spectroscopy measurements. The results of systematic measurements of magnetic AC susceptibility as a function of temperature and frequency are presented. We observed different types of magnetic behavior. For ZnO samples doped with low content of FeO, the results of low-field AC susceptibility are satisfactorily explained by superparamagnetic model including inter-particle interactions. With the increase of magnetic FeO content, the spin-glass-like behavior is observed
IV-VI ferromagnetic semiconductors recent studies
In some IV-VI semimagnetic semiconductors, the RKKY interaction can dominate over the standard d-d superexchange and become the driving mechanism for ion-ion coupling. In effect, for low hole concentrations the Mn ion system is in a paramagnetic phase, whereas for higher ones it reveals typical ferromagnetic behavior. In this paper, recent work on IV-VI ferromagnetic (SnMnTe, PbSnMnTe and GeMnTe) systems will be presented. In particular, the influence of the presence of two types of magnetic ions (transition metal: Mn and rare earth metal: Eu or Er) incorporated into a semiconductor matrix on magnetic properties of resultant semimagnetic semiconductor will be described
Raman Scattering from ZnO(Fe) Nanoparticles
Nanocrystalline samples of ZnO(Fe) were synthesized by wet chemical method. Samples were characterized by X-ray diffraction to determine composition of the samples (ZnO, Fe₂O₃, ZnFe₂O₄) and the mean crystalline size (8-52 nm). In this paper we report the experimental spectra of the Raman scattering (from 200 to ). Main characteristics of experimental Raman spectrum in 200 to spectral region are: sharp peak at and broad two-phonon structure at ≈ 700 cm^{-1}$ that has different position and shape in case of ZnFe₂O₄ or Fe₂O₃ nanoparticles