Fluctuating field model for conduction electron spin resonance in graphite

We outline a theory for conduction electron-spin resonance (CESR) in highly oriented pyrolytic graphite. The fundamental approximation is to treat the spin-orbit interaction as an effective field. In this approach, the shift in the g factor, which is associated with the mean value of the field, is related to the orbital susceptibility of the electrons. The linewidth comes from fluctuations in the effective field caused by the scattering of the electrons. The theory is used to interpret our CESR measurements.701

Antiferromagnetic ordering of divalent Eu in EuCu2Si2 single crystals

We report the synthesis, from an indium flux, of single crystals of EuCu2Si2. In contrast to previous studies of polycrystalline samples in which intermediate-valent behavior for Eu is reported, we find that in single crystals of EuCu2Si2 the behavior of Eu is divalent, including the presence of antiferromagnetic order at 10 K. The origins of these variations in ground-state properties are discussed in terms of effective chemical pressure and local changes in chemical environment.63

Neutral dangling bond depletion in amorphous SiN films induced by magnetic rare-earth elements

Amorphous silicon-nitrogen (a-SiN) thin films doped with rare-earth elements (RE = Y, La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, and Lu) were prepared by cosputtering and studied by means of electron spin resonance. It was found that the neutral dangling bond density, [D-0], of the a-SiN films decreases with the presence of magnetic REs and the drop in [D-0] approximately scales with the de Gennes and/or the spin factor of each RE element. Similar to the decrease in T-c in RE-doped superconductors, our experimental results strongly suggest that an exchange-like interaction, H similar to J(RE.D0)S(RE).S-D0, between the spin of the magnetic REs and that of the D-0 is taking place. (C) 2003 Published by Elsevier Ltd.12841700475

Simultaneous observation of the magnetic and electric behavior in a correlated system near a metal-semiconductor transition: ESR in pellets of conducting polymers

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Electron spin resonance (ESR) experiments show, at the metal-semiconductor transition temperature of a conducting polymer, the distinct contributions of the disordered and crystalline regions. In the more disordered regions of the polymer the polarons experience an antiferromagnetic coupling. As the level of disorder decreases, when small crystalline regions appear, there is a tendency, in some temperature range, for the polarons to interact ferromagnetically. For more ordered regions or crystalline regions of larger sizes, there is a competition between localized ferromagnetic coupled polarons and delocalized ones, that is, between localization and delocalization. The possibility to fit the ESR data for one of the samples using two Dysonian lines, one for each phase, allows one to follow the general behavior of the microwave conductivity as a function of the temperature. The semiconducting behavior of the disordered phase is clearly observed, as well as the true metallic behavior of the crystalline phase revealed by the increase in conductivity with the decrease in temperature.801Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Crystal field study in rare-earth-doped LuInNi4

Magnetic susceptibility and electron spin resonance experiments in the rare earth (R = Nd, Er, and Yb) 5-25% doped cubic intermetallic LuInNi4 enable estimates of the fourth A4 and sixth A6 order crystal-field parameters for this compound. These parameters yield a Γ6 doublet, a Γ7 doublet, and a Γ8 quartet as the ground states for Nd3+, Er3+, and Yb3+, respectively, and an overall crystal-field splitting of 100-300 K. The A4 and A6 parameters are found to have comparable order of magnitude for all the R studied and their values are in agreement with reported values for other cubic systems

Crystal field study in rare-earth-doped LuInNi4

Magnetic susceptibility and electron spin resonance experiments in the rare earth (R = Nd, Er, and Yb) 5-25% doped cubic intermetallic LuInNi4 enable estimates of the fourth A4 and sixth A6 order crystal-field parameters for this compound. These parameters yield a Γ6 doublet, a Γ7 doublet, and a Γ8 quartet as the ground states for Nd3+, Er3+, and Yb3+, respectively, and an overall crystal-field splitting of 100-300 K. The A4 and A6 parameters are found to have comparable order of magnitude for all the R studied and their values are in agreement with reported values for other cubic systems

Antiferromagnetic ordering of divalent Eu in EuCu2Si2 single crystals

We report the synthesis, from an indium flux, of single crystals of EuCu2Si2. In contrast to previous studies of polycrystalline samples in which intermediate-valent behavior for Eu is reported, we find that in single crystals of EuCu2Si2 the behavior of Eu is divalent, including the presence of antiferromagnetic order at 10 K. The origins of these variations in ground-state properties are discussed in terms of effective chemical pressure and local changes in chemical environment. © 2001 The American Physical Society

Crystal field study in rare-earth-doped LuInNi4

Magnetic susceptibility and electron spin resonance experiments in the rare earth (R = Nd, Er, and Yb) 5-25% doped cubic intermetallic LuInNi4 enable estimates of the fourth A(4) and sixth A(6) order crystal-field parameters for this compound. These parameters yield a Gamma (6) doublet, a Gamma (7) doubler, and a Gamma (8) quartet as the ground states for Nd3+, Er3+, and Yb3+, respectively, and an overall crystal-field splitting of 100-300 K. The A(4) and A(6) parameters are found to have comparable order of magnitude for all the R studied and their values are in agreement with reported values for other cubic systems.631

Antiferromagnetic ordering of divalent Eu in EuCu2Si2 single crystals

We report the synthesis, from an indium flux, of single crystals of EuCu2Si2. In contrast to previous studies of polycrystalline samples in which intermediate-valent behavior for Eu is reported, we find that in single crystals of EuCu2Si2 the behavior of Eu is divalent, including the presence of antiferromagnetic order at 10 K. The origins of these variations in ground-state properties are discussed in terms of effective chemical pressure and local changes in chemical environment. © 2001 The American Physical Society

Pattern changes of EEG oscillations and BOLD signals associated with temporal lobe epilepsy as revealed by a working memory task

Background: It is known that the abnormal neural activity in epilepsy may be associated to the reorganization of neural circuits and brain plasticity in various ways. On that basis, we hypothesized that changes in neuronal circuitry due to epilepsy could lead to measurable variations in patterns of both EEG and BOLD signals in patients performing some cognitive task as compared to what would be obtained in normal condition. Thus, the aim of this study was to compare the cerebral areas involved in EEG oscillations versus fMRI signal patterns during a working memory (WM) task in normal controls and patients with refractory mesial temporal lobe epilepsy (MTLE) associated with hippocampal sclerosis (HS). The study included six patients with left MTLE-HS (left-HS group) and seven normal controls (control group) matched to the patients by age and educational level, both groups undergoing a blocked design paradigm based on Sternberg test during separated EEG and fMRI sessions. This test consisted of encoding and maintenance of a variable number of consonant letters on WM. Results: EEG analysis for the encoding period revealed the presence of theta and alpha oscillations in the frontal and parietal areas, respectively. Likewise, fMRI showed the co-occurrence of positive and negative BOLD signals in both brain regions. As for the maintenance period, whereas EEG analysis revealed disappearance of theta oscillation, fMRI showed decrease of positive BOLD in frontal area and increase of negative BOLD in the posterior part of the brain. Conclusions: Generally speaking, these patterns of electrophysiological and hemodynamic signals were observed for both control and left-HS groups. However, the data also revealed remarkable differences between these groups that are consistent with the hypothesis of reorganization of brain circuitry associated with epilepsy