Detection of quasi-periodic processes in repeated measurements: New approach for the fitting and clusterization of different data

Many experimentalists were accustomed to think that any independent measurement forms a non-correlated measurement that depends weakly from others. We are trying to reconsider this conventional point of view and prove that similar measurements form a strongly-correlated sequence of random functions with memory. In other words, successive measurements "remember" each other at least their nearest neighbors. This observation and justification on real data help to fit the wide set of data based on the Prony's function. The Prony's decomposition follows from the quasi-periodic (QP) properties of the measured functions and includes the Fourier transform as a partial case. New type of decomposition helps to obtain a specific amplitude-frequency response (AFR) of the measured (random) functions analyzed and each random function contains less number of the fitting parameters in comparison with its number of initial data points. Actually, the calculated AFR can be considered as the generalized Prony's spectrum (GPS), which will be extremely useful in cases where the simple model pretending on description of the measured data is absent but vital necessity of their quantitative description is remained. These possibilities open a new way for clusterization of the initial data and new information that is contained in these data gives a chance for their detailed analysis. The electron paramagnetic resonance (EPR) measurements realized for empty resonator (pure noise data) and resonator containing a sample (CeO2 in our case) confirmed the existence of the QP processes in reality. But we think that the detection of the QP processes is a common feature of many repeated measurements and this new property of successive measurements can attract an attention of many experimentalists. © 2014 Elsevier B.V

Room temperature ferromagnetic-like response in “bulk” Y-doped CeO<inf>2</inf>

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimStrong ferromagnetic-like response is observed at room temperature in “bulk”- and nano-crystalline Y-doped CeO2. The saturation magnetization for “bulk” (∼600 nm) crystallites of CeO2 doped with 25 at.% Y is more than an order of magnitude higher compared to its nanocrystalline (∼10 nm) counterpart. High frequency electron spin resonance and 89Y nuclear magnetic resonance measurements indicate clustering of electronic defects in the “bulk” crystallites. The remarkable size dependence of the magnetic behavior likely originates from a collective magnetic response of defect-lined nanodomain interfaces in the “bulk” crystallites, consistent with the giant orbital paramagnetism model

Resonators ″loop-slot″ for pulse ESR spectrometers of 3 cm range

Constructions of two-loop ″loop-slot″-type resonators for pulse electron paramagnetic resonance spectrometers of 3 cm range are described. The resonators are characterized by 1 GHz frequency tuning and controlled connection with waveguide line. Microwave power which is necessary for optimum echo attainment at the usage of these resonators is shown to be by 10 db less than in a case of usual rectangular resonator

EPR study of nanocrystalline CeO<inf>2</inf> exhibiting ferromagnetism at room temperature

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Electron paramagnetic resonance (EPR) spectroscopy complemented with X-ray diffraction, X-ray fluorescence, and optical spectroscopy was used to study nanocrystalline CeO2 powder samples that exhibit weak room-temperature ferromagnetism. EPR lines assigned to the Ce3+ trigonal sites were found for the first time in cerium dioxide that contains a trace impurity of Mn2+. This finding indicates that manganese dopant facilitates the conversion of the oxidation state of Ce4+ to Ce3+ in nanocrystalline CeO2. Our results support the view that Ce3+/Ce4+ pairs along with defects on the surface of nanoparticles are responsible for the ferromagnetism in CeO2. The EPR study reveals that the charge-transfer mechanism proposed recently is more suitable to explain the origin of room-temperature ferromagnetism in CeO2 than the F+-centers exchange interactions

Application of Q-band electron spin echo spectrometer to investigation of glasses doped with rare earth ions

The Q-band electron spin echo (ESE) spectrometer which was created using modern microwave components is described. This simple incoherent apparatus was used with the X-band one for the study of phosphate and silicate glasses doped with non-Kramers rare earth Tb3+ ions. the EPR spectra measured by the ESE method have frequency independent peaks. The experimental results presumably show the existence of several types of paramagnetic centers in studied systems. © 1992 Springer

Spatial distribution of Nd3+ dopant ions in vitreous silica: A pulsed electron paramagnetic resonance spectroscopic study

The structural aspects of clustering of Nd3+ ions in Nd2O3-doped SiO2 glasses and the effect of Al3+ codoping on these clusters have been investigated with pulsed electron paramagnetic resonance (EPR) techniques over a temperature range of 1.5-4 K. The Nd2O3 concentrations in these glasses range between 700 and 2400 ppm by weight. The Nd3+ echo-detected EPR (EDEPR) spectra of the Al-free glasses show indications of weak exchange coupling between Nd3+ ions due to clustering. The EDEPR spectra also suggest that the local coordination environment of Nd3+ ions is affected by codoping with Al. The electronic spin-lattice relaxation rates are found to be not sensitive to the spatial distribution of Nd3+ ions over the entire temperature range of measurements. On the other hand, the concentration dependence of phase relaxation rates show clear evidence of clustering of Nd3+ ions in Al-free glasses, even at the lowest Nd2O3 doping levels. These Nd3+ clusters are found to break up and homogenize with an increase in the average Nd-Nd distance on codoping with Al. Analyses of the hyperfine sublevel correlation spectrum of a Nd and Al codoped glass indicate that the homogenization of Nd3+ clusters is possibly a consequence of the formation of Nd-O-Al linkages. © 2001 American Institute of Physics

Direct spectroscopic observation of the atomic-scale mechanisms of clustering and homogenization of rare-earth dopant ions in vitreous silica

Structural aspects of clustering of rare earth ions in oxide glasses have been studied for the last several years in relation to their applications in photonics. However, the mechanism of homogenization of the spatial distribution of rare earth ions by codoping, typically with Al or P, is still not well understood. In this work we report direct experimental determination of the homogenization mechanism of Yb3+ ion clusters in silica glasses doped with 0.1 wt. % Yb2 O3 and codoped with Al or P, using two-dimensional HYSCORE-EPR spectroscopy. The results lead us to conclude that Yb creates its coordination environment via formation of Yb-O-Si and Yb-O-Yb bonds in a Yb-doped silica glass and even the light codoping with Al starts replacing these bonds with Yb-O-Al linkages. Heavy codoping with P replaces all Yb-O-Si Yb linkages with Yb-O-P linkages. The formation of a next-nearest neighbor shell of Al or P creates suitable structural pockets, which ultimately leads to homogenization. © 2006 The American Physical Society

Spectroscopic study of the effect of N and F codoping on the spatial distribution of Er3+ dopant ions in vitreous SiO2

Pulsed electron paramagnetic resonance (EPR) spectroscopy has been used to study the influence of codoping with N and/or F on the clustering of Er 3+ ions in vitreous SiO2. Measurements of echo-detected EPR, spin-lattice and phase memory relaxation times, and electron spin-echo envelope modulation (ESEEM) were made in the X band. Er-N, Er-F, and Er-N-F codoped glasses show clear evidence of clustering of Er3+ ions at concentration levels ranging between 6.67 × 1018 cm -3 and 6.67 × 1019 cm-3. However, the relatively long phase memory relaxation time and the observability of ESEEM in the Er-N-F codoped glass strongly indicate that combined codoping with N and F is more effective in homogenization of the spatial distribution of Er 3+ ions in vitreous SiO2, although, the structural mechanism remains unclear. The ESEEM results provide evidence in favor of the presence of N in the vicinity of the Er3+ ions in Er-N-F codoped vitreous SiO2. © 2007 American Institute of Physics

The Jahn-Teller effect in Cr5+-doped PbTiO3: A multi-frequency electron paramagnetic resonance study

Electron paramagnetic resonance (EPR) spectra of Cr5+ defects incorporated on Ti4+ sites in powdered ceramics of PbTiO3 were investigated in the temperature range 50-400K at 9GHz (X), 34GHz (Q) and 94GHz (W band). The Jahn-Teller effect stabilizes the vibronic ground state of the 3d1 electron of the Cr5+ ion and leads to a tetragonally distorted defect- O6 octahedron with the point symmetry D4h. The spontaneous electrical polarization present in the ferroelectric phase of PbTiO3 appears as a further perturbation producing an additional g-tensor contribution by the quadratic field effect. Its symmetry is dependent on the orientation of the electrical polarization with respect to the Jahn-Teller distortion axis, the tetragonal axis of the defect- O6 octahedron. If the polarization of a domain is anti-or parallel to this axis, the local tetragonal symmetry of the Cr5+ ion persists whereas it is reduced by a perpendicular orientation. Anisotropic EPR spectra of tetragonally and orthorhombic distorted Cr5+O6 12- are detected at low temperatures. Increasing the temperature, the peaks of the two spectra are broadened and a motionally averaged isotropic spectrum appears at 200K. © 2010 IOP Publishing Ltd

A pulsed EPR study of clustering of Yb3+ ions incorporated in GeO2 glass

The structural aspects of clustering of Yb3+ ions and the paramagnetic behavior of these clusters have been investigated in GeO 2 glasses doped with 140-1100 ppm by weight of Yb2O 3 using time-domain electron paramagnetic resonance (EPR) spectroscopic techniques. The echo-detected EPR (EDEPR) spectra of Yb 3+ ions and their unusual dependencies on microwave power and magnetic field have been found to be indicative of the formation of clusters of these rare earth ions in GeO2 glass that behave as non-Kramers type spin systems. The magnetic field and concentration dependence of phase relaxation rates of Yb3+ in these glasses further substantiate such a scenario and indicate the formation of clusters of Yb3+ ions. A comparison of the EDEPR spectra with calculated cw-EPR line shapes yields a semi-quantitative measure of the typical cluster size of ≥3 Yb atoms and intra-cluster Yb-Yb distances of 3.5-4.0 Å in these glasses at doping levels of ≥350 ppm of Yb2O3. © 2003 Elsevier B.V. All rights reserved