Papers by Keyword: Electron Spin Resonance

Abstract: Cavity measurements of a high frequency (60 GHz) electron spin resonance (ESR) have been carried our for a single crystal of EuB6 at temperatures 4.2-50K in magnetic field up to 7 T, which has been aligned along [001] crystallographic direction. The influence of the experimental geometry on the parameters of the resonance line has been studied. It is found that in conditions of a homogeneous magnetic field the ESR spectrum in EuB6 is formed by a single resonance line at all temperatures including the ferromagnetic ordering region. The presence of the gradient of the magnetic field in the sample causes strong broadening of the resonance line at low temperatures and even may induce a double peak ESR structure. The analysis of the linewidth temperature dependence in EuB6 shows the anomalous growth of the line width below Curie temperature TC ~15 K.

Abstract: In this report the results on the investigation of magnetic states of Fe and Co ions in superlattice [Mo(12Å)Co(21Å)Fe(14Å)]*100 are presented. The magnetic superlattices were obtained by means of cathode sputtering in discharge with oscillating electrons. The results of X-ray diffraction show that magnetic superlattices (MSL) have amorphous state. The magnetic states of Fe and Co ions were investigated using Mössbauer spectroscopy (MS) and electron spin resonance (ESR) for the as-deposited MSL and after annealing at 450°C. The results of our studies of Fe and Co ions states indicate that they correspond to high-spin states in clusters Fen, Com, FenCom, FenMom with small number of atoms n, m in clusters.

Abstract: We report the first direct experimental evidence of the presence of antiferromagnetic dimers in VOx nanotubes based on the high frequency (60 GHz) electron spin resonance study carried out in the temperature range of 4.2-200 K. Arguments favouring a possible observation of the low temperature quantum critical phenomena in VOx nanotubes are provided.

Abstract: Polycarbonate - carbon nanofibers, containing various concentrations of filler ranging from 0 % to 10 % wt. have been investigated by electron spin resonance. The as obtained electron spin resonance spectra are complex due to the overlap of several resonances originating from the conducting electrons delocalized over the metallic domains of nanotubes, from the free radicals generated within the polymeric matrix during the processing step, from insulating graphite particles, and from catalyst residues (observed as magnetic impurities). The effect of the filler on the resonance line shape is analyzed in detail. The shape of resonance spectrum demonstrates that the resonance line located near g=2.00 originates from conducting electrons delocalized over the metallic domains of nanotubes. Thos line was accurately fitted by a Lorentzian line shape.

Abstract: Measurements of conduction electron spin resonance (CESR) in steel allow to separate the contributions from free electrons which provide the metallic character of interatomic bonds and from localized electrons involved in the covalent bonds. The data of the CESR study carried out on austenitic CrMn steels alloyed with carbon, nitrogen or carbon+nitrogen are presented. It is shown that, in contrast to carbon, nitrogen enhances the metallic character of atomic interactions with a maximum of the concentration of free electrons at some critical content of nitrogen (about 2 at.%). The combined alloying with carbon+nitrogen leads to two effects: (i) a larger concentration of free electrons and (ii) a shift of the critical content of interstitials towards higher values. The experimental data are supported by theoretical ab initio calculations of the electron properties of austenitic CrMn steels alloyed with carbon, nitrogen or carbon+nitrogen. Using the full-potentialfull- electron-linearized-augmented-plane-wave (FLAPW) method, the total energy per primitive crystal cell, the density of the electron states (DOS) and the distribution of the electron density over the crystal lattice were calculated by means of the computational program WIEN-2k. The total electron energy decreases due to alloying in the sequence of carbon→nitrogen→carbon+nitrogen, which suggests a corresponding increase in the thermodynamic stability of the austenite. The obtained results of the theoretical and experimental studies of the electron structure were used for the development of super-high–strength stainless austenitic steels.

Abstract: Utilizing an very sensitive electron spin resonance (ESR) technique, spin dependent recombination (SDR) we have identified interface and near interface trapping centers in 4H and 6H SiC/SiO2 metal oxide semiconductor field effect transistors (MOSFETs). We extend our group’s earlier observations on 6H devices to the more technologically important 4H system and find that several centers can play important roles in limiting the performance of SiC based MOSFETs.