Search

In the present paper, we present an electron magnetic resonance (EMR) study of Ni 50.2 Mn 28.3 Ga 21.5 powders obtained from melt-spun ribbons in the milling process. We registered EMR spectra in various temperatures at the X-band. In the EMR spectra recorded for the samples taken at the beginning of the milling process, the "training effect" was observed. After 2 h of milling, this phenomenon was no longer observed. To determine the basic EMR parameters, such as linewidth, resonance field, and asymmetry parameters, the experimental data were fitted using a single metallic Lorentz line. In high-temperature regions, we observed the influence of dispersion on the shape of the spectra, but as the temperature decreased, the asymmetry of line was reduced. The shift in the resonance field value at high temperatures and the temperature dependence of the linewidth below Curie temperature indicate that the investigated samples exhibited a characteristics of a spin-glass alloy. [ABSTRACT FROM AUTHOR]

The article presents an electron magnetic resonance study of metal paints in terms of identification and selection of appropriate pigment components based on the summation of spectral components. Research was carried out to assess the durability of paints on the basis of the detection of free radicals in individual components, the occurrence of which leads to paint degradation. Two types of acrylic resins, three types of organic pigments, and titanium white, hardener, and clearcoat were tested. The g-factor as well as all electron magnetic resonance line parameters were calculated. Electron magnetic resonance is found to be useful in the effort to eliminate a paint component that reduces color durability and to select components in terms of paint quality. [ABSTRACT FROM AUTHOR]

Magnetic parameters of magnetosomes inside the bacteria of MSR-1, LBB-42, AMB-1, SP-1, BB-1, and SO-1 strains of the genus Magnetospirillum fixed by 5% formalin in the nutrient medium were estimated by measurements of the nonlinear longitudinal response to a weak ac magnetic field (NLR-M2) at room temperature. For the BB-1, MSR-1, and AMB-1 strains, the measurements of the electron magnetic resonance (EMR) spectra with the special X-band spectrometer for wide-line registration were also carried out. To trace the evolution of the magnetic state of the magnetosomes during the long-term storage, freshly prepared samples ("new") and samples after a year of storage at 4 °C ("old") were studied. The assessment of the state of the bacteria ensemble in the medium after the long-term storage was carried out for one typical strain (BB-1) using atomic force microscopy. The stable single-domain state of magnetic centers in the magnetosomes indicating their proximity to a superparamagnetic (SPM) regime was found at the scan frequency 0.02 Hz of the steady magnetic field. This allowed a semi-quantitative analysis of M2 data to be carried out with the formalism based on the numerical solution of the kinetic Fokker–Planck equation for SPM particles. Processing the NLR-M2 data demonstrated the presence of two kinds of magnetosomes in both the "new" and "old" samples: (i) those with the large magnetic moment (the "heavy", monodisperse mode) and (ii) those with the comparatively small magnetic moment (the "light", highly dispersed mode). The EMR spectra were formed mostly by the "heavy" fraction for both samples. The presence of two peaks in the spectra evidenced the presence of conventional uniaxial magnetic anisotropy in the magnetosomes. The appearance of one or two additional peaks in the spectra in the "old" fraction of some strains implied their instability at the long-term storage, even when fixed by formalin and sealed in the nitrogen atmosphere. [ABSTRACT FROM AUTHOR]

The material with a high Curie temperature of cobalt-doped zinc oxide embedded with silver-nanoparticle thin films was studied by electron magnetic resonance. The nanoparticles were synthesized by the homogeneous nucleation technique. Thin films were produced with the pulsed laser deposition method. The main aim of this work was to investigate the effect of Ag nanoparticles on the magnetic properties of the films. Simultaneously, the coexisting Ag0 and Ag2+ centers in zinc oxide structures are shown. A discussion of the signal seen in the low field was conducted. To analyze the temperature dependence of the line parameters, the theory described by Becker was used. The implementation of silver nanoparticles causes a significant shift of the line, and the ferromagnetic properties occur in a wide temperature range with an estimated Curie temperature above 500 K. [ABSTRACT FROM AUTHOR]

Magnetic parameters of magnetosomes inside the bacteria of MSR-1, LBB-42, AMB-1, SP-1, BB-1, and SO-1 strains of the genus Magnetospirillum fixed by 5% formalin in the nutrient medium were estimated by measurements of the nonlinear longitudinal response to a weak ac magnetic field (NLR-M2) at room temperature. For the BB-1, MSR-1, and AMB-1 strains, the measurements of the electron magnetic resonance (EMR) spectra with the special X-band spectrometer for wide-line registration were also carried out. To trace the evolution of the magnetic state of the magnetosomes during the long-term storage, freshly prepared samples (“new”) and samples after a year of storage at 4 °C (“old”) were studied. The assessment of the state of the bacteria ensemble in the medium after the long-term storage was carried out for one typical strain (BB-1) using atomic force microscopy. The stable single-domain state of magnetic centers in the magnetosomes indicating their proximity to a superparamagnetic (SPM) regime was found at the scan frequency 0.02 Hz of the steady magnetic field. This allowed a semi-quantitative analysis of M2 data to be carried out with the formalism based on the numerical solution of the kinetic Fokker–Planck equation for SPM particles. Processing the NLR-M2 data demonstrated the presence of two kinds of magnetosomes in both the “new” and “old” samples: (i) those with the large magnetic moment (the “heavy”, monodisperse mode) and (ii) those with the comparatively small magnetic moment (the “light”, highly dispersed mode). The EMR spectra were formed mostly by the “heavy” fraction for both samples. The presence of two peaks in the spectra evidenced the presence of conventional uniaxial magnetic anisotropy in the magnetosomes. The appearance of one or two additional peaks in the spectra in the “old” fraction of some strains implied their instability at the long-term storage, even when fixed by formalin and sealed in the nitrogen atmosphere.

Some relevant aspects of Electron Paramagnetic Resonance (EPR) applied to the fields of surface chemistry and heterogeneous catalysis are illustrated in this perspective paper that aims to show the potential of these techniques in describing critical features of surface structures and reactivity. Selected examples are employed covering distinct aspects of catalytic science from morphological analysis of surfaces to detailed descriptions of chemical bonding and catalytic sites topology. In conclusions the pros and cons related to the acquisition of EPR instrumentations in an advanced laboratory of surface chemistry and heterogeneous catalysis are briefly considered. [ABSTRACT FROM AUTHOR]

In the present study, zero field splitting (ZFS) parameters are investigated for Mn(II) ion doped perovskites, viz. PbTiO 3 , BaTiO 3 and SrTiO 3 . The ZFS parameter and magnetisation induced in the host are investigated using quantum mechanical perturbation theory and classical statistics. A mathematical derivation is proposed to study magnetisation and ZFS due to charge distribution generated electric field and spin–orbit coupling (SOC). The computation of ZFS parameters is performed using non-hybrid functional unrestricted Kohn–Sham (UKS). The mathematical formulation is valid for perovskites in the non-ferroelectric state and finite temperature range. The contour plot and mesh surface of the spin–orbit interaction and induced magnetisation are reported. [ABSTRACT FROM AUTHOR]

Iron-gallium borate, Fe x Ga 1− x BO 3 , single crystals have been synthesized by the solution in the melt technique. The exact x -values in the crystals have been determined by X-ray fluorescence analysis and checked by Energy Dispersive X-Ray Spectroscopy. Scanning Electron Microscopy has been used to map distributions of iron and gallium ions in the crystals. The electron magnetic resonance (EMR) spectra as well as field and temperature dependences of the magnetization obtained by SQUID reveal the existence of different magnetic phases in different x ranges, viz. weakly ferromagnetic antiferromagnetic, magnetic cluster and paramagnetic phase. For crystals with 0.32 ≤ x ≤ 0.83, the Néel temperatures, T N , have been determined. The magnetometry of these crystals suggests the existence of another magnetic transition at a temperature well below T N , tentatively ascribed to a Morin type transition. Detailed EMR and SQUID studies of the crystal with x ≈ 0.2 reveal the existence of magnetic nanoclusters showing superparamagnetic behaviour. Using a laboratory developed code based on the Monte-Carlo technique, spatial distributions of dia- and paramagnetic ions in the crystal with x ≈ 0.2 has been visualized and possible cluster sizes have been estimated. • Fe x Ga 1− x BO 3 can be weakly ferro- antiferromagnetic, superpara- or paramagnetic. • Superparamagnetism in magnetically diluted crystals arises from magnetic clusters. • Fe x Ga 1− x BO 3 are promising as fine-tunable materials for advanced applications. [ABSTRACT FROM AUTHOR]

The aim of this study is the application of electron magnetic resonance (EMR) spectroscopy to determine the interactions between NaY and HY zeolites and Cu-Mn-Zn spinels loaded onto the zeolite surfaces. The materials were characterized using XRD and IR spectroscopies. Four types of EMR lines were observed for Cu-Mn-Zn/NaY, Cu-Mn-Zn/HY samples. The difference between the EMR spectra recorded at 77 and 293 K has been shown. The spectra recorded at 77 K allowed us to distinguish between the species formed on NaY and HY zeolites. The EMR spectrum of Cu-Mn-Zn/NaY recorded at 77 K showed only one line attributed to antiferromagnetic spinels Cu1.4Mn1.6O4 and ZnMn2O4 or/and Cu0.5Zn0.5Mn2O4. The spinels appeared to be more stable (more strongly attached) on HY zeolite than on NaY one. It was proved that different strength of interactions between the zeolites and Cu-Mn-Zn spinels was caused by differences in the acidity of NaY and HY zeolites.

Electron magnetic resonance (EMR) spectra of gadolinium-doped barium titanate (BaTiO3) have been studied at room temperature for gadolinium concentrations between 0.20 and 2.00 mol%. The results suggest that the Gd3+ ions occupy substitutional sites, replacing the Ba2+ ion, that the electron magnetic resonance linewidth increases with increasing gadolinium concentration, and that the range of the exchange interaction between Gd3+ ions is about 0.98 nm, of the same order as that of the same ion in other host lattices, such as strontium titanate (SrTiO3), strontia (SrO), quicklime (CaO), magnesia (MgO) and zircon (ZrSiO4). The fact that the electron magnetic resonance linewidth of the Gd3+ ion increases, regularly and predictably, with Gd concentration, shows that the Gd3+ ion can be used as a probe to study, rapidly and non-destructively, the crystallinity and degradation of BaTiO3.

Abstract A remarkable characteristic of borate glasses is the ability of forming magnetic nanoparticles at low doping with transition element oxides. We have studied structure and magnetic properties of iron oxide nanoparticles formed in borate glasses, in particular, concentration and temperature dependences of magnetic circular dichroism (MCD) and electron magnetic resonance (EMR) spectra. A series of glasses of molar composition 22.5K 2 O-22.5Al 2 O 3 –55B 2 O 3 doped with 1.5 mass % of Fe 2 O 3 and different contents of Gd 2 O 3 from 0.1 to 1.0 mass % was prepared using a conventional melt quenching technique and subjected to an additional thermal treatment. The whole set of results allows to identify the predominant magnetic phase in these glasses as ε-Fe 2 O 3 nanoparticles, with a considerable part of iron ions substituted by gadolinium. Analysis and computer simulations of the EMR spectra allow separating the contribution of electron paramagnetic resonance of diluted iron ions and together with the temperature dependences of magnetization demonstrate a superparamagnetic character of the nanoparticle magnetism. Highlights • Magnetic nanoparticles arise in borate glasses co-doped with Fe2O3 and Gd2O3. • The predominant magnetic phase in nanoparticles is identifies as ε-Fe 2 O 3. • A part of iron ions is substituted by gadolinium • MCD and EMR spectra of the glasses are obtained. • Computer analysis of the glasses EMR spectra is carried out [ABSTRACT FROM AUTHOR]

We have studied magnetic properties of zinc oxide (ZnO) composite doped with Co ions. The samples were obtained by pulsed laser deposition (PLD) method. Electron magnetic resonance (EMR) measurements were carried out and temperature dependence of EMR spectra was obtained. Analysis of temperature dependence of the integral intensity of EMR spectra was carried out using Curie-Weiss law. Reciprocal of susceptibility of an antiferromagnetic (AFM) material shows a discontinuity at the Néel temperature and extrapolation of the linear portion to negative Curie temperature. The results of temperature dependence of EMR spectra for the ZnO:Co sample and linear extrapolation to the Curie-Weiss law indicated the AFM interaction between Co ions characterized by the Néel temperatures TN = 50 K and TN = 160 K for various samples. The obtained g-factor is similar to g-factors of nanocrystals presented in literature, and the results confirm that in the core of these nanocrystals Co was incorporated as Co2+, occupying Zn2+ sites in wurtzite structure of ZnO. [ABSTRACT FROM AUTHOR]

The oxygen-deficient polycrystalline LaSrMnO (0 < γ ≤ 0.2) manganites were studied by electron magnetic resonance (EMR). The EMR spectra provide evidence for an unusual and γ-dependent transition of manganites from the ferromagnetic phase to the paramagnetic phase. A Griffiths phase, which reveals itself in the coexistence of ferromagnetic and paramagnetic resonance signals at a temperature significantly higher than the magnetic ordering temperature, was found in samples with 0.1 ≤ γ ≤ 0.2. The formation of this phase, characterized by the presence of ferromagnetic clusters in a paramagnetic matrix, is due to an oxygen deficiency that hinders realization of long-range ferromagnetic ordering of the manganese ions. [ABSTRACT FROM AUTHOR]

Electron magnetic resonance (EMR) spectra of Cr3+ ions in samples of chromium-doped strontium titanate (SrTiO3) have been studied at room temperature for chromium concentrations between 0.20 and 1.00 mol%. According to previous studies, chromium substitutes Ti4+ sites in the lattice and its preferred valence state is Cr4+, which is EMR silent in the X-band, but the trivalent state can be produced by illumination or codoping with Nb. In the present work, the codoping method was used; the results show the electron magnetic resonance linewidth of the Cr3+ spectrum increases with increasing chromium concentration and that the range of the exchange interaction between Cr3+ ions is about 0.96 nm.

We report the first successful synthesis of iron borate films. FeBO 3 films on GaBO 3 single crystal substrates have been prepared by a liquid phase epitaxy route. In order to determine optimal crystallization regimes, a series of experiments has been carried out. Electron microscope studies have allowed monitoring different phases of the film formation. The compositions of the film and of the substrate have been determined by energy-dispersive spectroscopy. X-ray diffraction analysis has allowed an accurate determination of a mismatch between the lattice parameters of the film and of the substrate. Electron magnetic resonance studies of the FeBO 3 film confirm the existence of magnetic ordering. The values of the effective Dzyaloshinskii field as well as the Néel temperature are in good accordance with those previously determined for FeBO 3 single crystal. [ABSTRACT FROM AUTHOR]

Low frequency electron paramagnetic resonance (LFEPR) spectrometers operating between 100 and 500 MHz typically have large-volume magnets that accommodate large samples. LFEPR spectroscopy with a 2.9 mm diameter surface coil was used to record point spectra and image the spatial distribution of the spin probe 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and electrophotographic toner in printed letters on a flat surface. The location of the surface coil was fixed on the desired location when a spectrum was recorded. The magnetic field of the spectrometer was fixed on the location of the signal and the sample was scanned under the surface coil in parallel trajectories to produce an image of the signal in the letters “LFEPR”. We speculate on the utility of this technique to study flat objects such as paintings and illuminated manuscripts with cultural heritage significance. [ABSTRACT FROM AUTHOR]

A new type of magnetic nanoparticles was revealed in borate glasses co-doped with low contents of iron and gadolinium. Structure and magnetic properties of the particles differ essentially from that of the α-Fe 2 O 3 , γ-Fe 2 O 3 , or Fe 3 O 4 nanoparticles which were detected earlier in similar glass matrices. Transmission electron microscopy including STEM-HAADF and EDX, synchrotron radiation-based XRD, static magnetic measurements, magnetic circular dichroism, and electron magnetic resonance studies allow referring the nanoparticles to the iron oxide phase-ε-Fe 2 O 3 . Analysis of the data set has shown that it is Gd atoms that govern the process of nanoparticles’ nucleation and its incorporation into the particles in different proportions can be used to adjust their magnetic and magneto-optical characteristics. [ABSTRACT FROM AUTHOR]

Since the first EPR/ESR spectrum of a paramagnetic substance was published over 70 years ago, the technical improvements did not occur until after/during World War II with the advent of radar technology. The approaches to biomedical problems started somewhat later with the real burst of activity starting after the birth of the spin label technique about 50 years ago. The applications to proteins, then membranes and nucleic acids, and later applications to cells and eventually in-vivo on small animals and now humans has led EPR/ESR to finally being recognized as a uniquely powerful technique in the toolbox of techniques probing macromolecules and their interactions, free radical biology and its eventual value as a diagnostic technique. This article gives an overview of EPR/ESR studies of biomedically related systems, including proteins and enzymes. It presents a very personal historical perspective, briefly reviews the origins of the technique and reflects on possible future directions. As with NMR, advances in molecular biology and technology drastically changed the nature and focus of the technique, particularly the site directed spin labeling method that has been invaluable in determining protein and macromolecular structure by both EPR and NMR. [ABSTRACT FROM AUTHOR]

The magnetic separator with the membrane separating unit made of laser-perforated thick ferromagnetic foil was tested using composite water suspension of magnetic nanoparticles adsorbed on hydroxylapatite microparticles. The average sizes of the particles in the suspension and the magnetic moment of the suspension were measured by dynamic light scattering and electron magnetic resonance correspondingly to evaluate the efficiency of the separation. It was shown experimentally that the separation is effected by the membrane type and the flow rate. Magnetic coarse grains (larger than 1 μm) were captured by the membrane preferably and the magnetic moment of the suspension decreased by 20–25% after the separation. The magnetic field simulation and experimental results demonstrate the higher separation efficiency for thicker membranes. [ABSTRACT FROM AUTHOR]

Based on the relation between quantum mechanical concepts such as effective Hamiltonians (EHs), perturbation theory (PT), and unitary transformations, and phenomenological aspects of spin Hamiltonians (SHs), the present tutorial tries to address the basics of the SH formalism. Using simple physical models and historical important examples, we have reviewed the derivation methods and applications of the SHs for a brief and in-depth description of various sources of anisotropies and interactions such as electronic (EZ), and nuclear Zeeman (NZ), terms, electron-exchange interaction (EE), zero-field splitting (ZFS), spin-spin (SS), spin-orbit (SO), nuclear quadrupole (NQ), and hyperfine couplings (HFCs), in a step-wise manner. In this way, this tutorial is tailored for the graduate students and young researchers who intend to begin their studies in the field of magnetism, electron magnetic resonance (EMR), spectroscopy, and related areas. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Magnetoferritin molecules with an average inorganic core diameter of 5.7±1.6nm and polycrystalline internal structure were investigated by a combination of transmission electron microscopy, magnetic susceptibility, magnetization, and electron magnetic resonance (EMR) experiments. The temperature and frequency dependence of the magnetic susceptibility allowed for the determination of the magnetic anisotropy on an experimental time scale which spans from seconds to nanoseconds. In addition, angle-dependent EMR experiments were carried out for the determination of the nanoparticle symmetry and internal magnetic field. Due to the large surface to volume ratio, the nanoparticles show larger and uniaxial rather than cubic magnetic anisotropies compared to bulk maghemite and magnetite. [Copyright &y& Elsevier]

The simple amino acid l-α-alanine (ala) in polycrystalline form was among the first substances to be proposed and subsequently developed for Electron Paramagnetic Resonance (EPR)-based solid state radiation dosimetry. One disadvantage with ala is a relatively low sensitivity for doses below a few gray (Gy) which is a dose range of particular interest in medical, accident and environmental applications. A number of other compounds have been screened and some of these have shown a better sensitivity to radiation exposure than ala , in some cases up to a factor of 7–8. In particular ammonium tartrate (AT) and lithium formate (LiFo) have been taken into practical use. The present work was initially aimed to investigate the low-temperature radical products in AT, and the reactions leading to the product of dosimetric interest at room temperature. As a part of these studies, the previously characterized major room temperature radical product was re-investigated using single crystal electron magnetic resonance (EMR) techniques combined with periodic density functional theory (DFT) -type quantum chemical calculations. Surprisingly, this study showed that the molecular structure of the dominant radical at room temperature is somewhat different from that previously proposed. Furthermore, a second room temperature radical, previously not well characterized, was carefully investigated and three hyperfine coupling tensors were determined. These three tensors were sufficient to simulate all experimental observations for the second radical but not alone sufficient to permit an unambiguous molecular structure of the defect to be determined. It appears that the EPR resonance from this radical does not influence the dosimetric potential of AT. • Two radicals, R1 and R2 , were observed in irradiated ammonium tartrate dihydrate crystals at RT. • Radical R1 was shown to exhibit a structure different from that previously published. • The revised structure for R1 is supported by periodic DFT-calculations. • Radical R2 was characterized in terms of three proton hyperfine coupling tensors. • The EPR resonance from R2 does not influence the resonance due to R1. [ABSTRACT FROM AUTHOR]

Highlights: [•] Orthorhombic monovalent doped manganites Pr0.6Sr0.4-xKxMnO3 (x = 0.05 to 0.2). [•] Unit cell volume decreases with K content. [•] Curie temperature decreases with K content. [•] Electron magnetic resonance determines low temperature limit of paramagnetic phase. [ABSTRACT FROM AUTHOR]