Defect properties of cobalt-doped hexagonal barium titanate ceramics
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X-ray diffraction (XRD) patterns, electron paramagnetic resonance (EPR) powder spectra (9 and 34 GHz) and the magnetic susceptibility of BaTiO3 + 0.04 BaO + x/2 Co2O3 (0.001 ⩽ x ⩽ 0.02) ceramics were studied to investigate the incorporation of Co ions in the BaTiO3 lattice and their valence states as well as the development of the hexagonal phase (6H modification) in dependence on doping level x and sintering temperature Ts. At Ts = 1400 °C the 6H modification begins to occur at a nominal Co concentration x of about 0.001 and for x > 0.005 the samples are completely hexagonal at room temperature. Two different EPR spectra were observed in the 6H modification of BaTiO3, which were both assigned to paramagnetic Co(2+) ions located at the two crystallographically non-equivalent Ti sites in 6H-BaTiO3. The EPR g tensor values as well as the molar paramagnetic susceptibility, measured in the temperature range 5 K-300 K at a magnetic field of 9 T, were analyzed in the framework of the ligand field theory using the program CONCORD. The combination of EPR and magnetic measurements reveals that in air-sintered 6H BaTiO3, the incorporated Co occurs as a mixture of paramagnetic Co(2+) and diamagnetic Co(3+) ions, whereas in samples annealed in reducing atmosphere the majority of Co is in the divalent state. The occurrence of Co(4+) can be excluded for all investigated samples. The sample color caused by Co(2+) and Co(3+) ions is beige/light yellow and dark grey/black, respectively. The majority of the Co(2+) ions substitutes Ti in the exclusively corner-sharing oxygen octahedra possessing nearly cubic symmetry. The corresponding ligand field parameter [Formula: see text] amounts to about -28 000 cm(-1) (Wybourne notation, 10Dq ≈ 20 000 cm(-1)). In the reduced samples nearly 5% of the detected Co(2+) ions occupy the Ti site in the face-sharing oxygen octahedra, which are significantly trigonally distorted. The negative sign of the obtained ligand field parameter [Formula: see text] ≈ -7300 cm(-1) reflects a compression of this octahedron in direction of the hexagonal c-axis.Keywords:
Diamagnetism
Barium titanate
Atmospheric temperature range
It is commonly believed that a paramagnetic rod will align itself with an impressed magnetic field and that a diamagnetic rod will set its long dimension across the field. The present paper shows that this conception is not generally valid. In a strictly uniform field both paramagnetic and diamagnetic rods will set themselves parallel to the field. In a nonuniform field the orientation of each of these rods will depend upon the particular configuration of the field.
Diamagnetism
Rod
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The electronic energy of H + 2 in magnetic fields of up to B = 0.2B 0 (or 4.7 ×10 4 Tesla) is investigated.Numerical values of the magnetic susceptibility for both the diamagnetic and paramagnetic contributions are reported for arbitrary orientations of the molecule in the magnetic field.It is shown that both diamagnetic and paramagnetic susceptibilities grow with inclination, while paramagnetic susceptibility is systematically much smaller than the diamagnetic one.Accurate two-dimensional Born-Oppenheimer surfaces are obtained with special trial functions.Using these surfaces, vibrational and rotational states are computed and analysed for the isotopologues H + 2 and D + 2 .
Diamagnetism
Isotopologue
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Electron paramagnetic resonance (EPR) spectroscopy is the method of choice for the study of paramagnetic systems with unpaired electron spins. It is in particular successful in case of magnetically diluted solids where EPR methods allow a detailed exploration of structural and electronic properties of the paramagnetic centers. We present an introduction in the basic principles of continuous-wave EPR spectroscopy of porous materials and introduce briefly more recently established pulsed EPR experiments in the first part. Selected application examples of EPR methods for the investigation of paramagnetic species in metal–organic framework materials are discussed and reviewed in the second part. They involve the spectroscopic characterization of paramagnetic framework transition metal ions, paramagnetic adsorption complexes, and radical species.
Unpaired electron
Pulsed EPR
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An expression is derived for the magnetic susceptibility of an intrinsic semiconductor in a tight-binding basis that is valid for both crystalline and amorphous materials. In addition to diamagnetic intraband terms proportional to the square of the tight-binding radii there are interband terms involving intersite matrix elements. These additional terms are evaluated for a simple two-band model and found to be paramagnetic. It is shown that in an amorphous material these paramagnetic intersite contributions will be reduced, thereby producing a diamagnetic enhancement.
Diamagnetism
Tight binding
Matrix (chemical analysis)
Amorphous semiconductors
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Diamagnetism
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We report magnetic measurements up to 1100 K on a multi-walled carbon nanotube mat sample using a Quantum Design vibrating sample magnetometer. In an ultra-low field (H = -0.02 Oe), we find a very large paramagnetic susceptibility (up to 12.7% of 1/4pi) at 1100 K and a very large diamagnetic susceptibility (at least 8.4% of -1/4pi) at 482 K. A small magnetic field (2.1 Oe) completely suppresses the diamagnetic susceptibility at 482 K and reduces the paramagnetic susceptibility at 1100 K by a factor of over 20. We rule out explanations based on magnetic contaminants, instrument artifacts, and orbital diamagnetism. The magnetic data are inconsistent with any known physical phenomena except for granular superconductivity. The present results suggest the existence of an unknown new physical phenomenon or superconductivity with an ultra-high transition temperature.
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Diamagnetism
Magnetism
Magnetic impurity
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Natural sepiolite minerals and their γ -irradiated forms were investigated by electron paramagnetic resonance (EPR) at room temperature and at 113 K. The EPR signals in powders of natural sepiolite were observed due to clusters of Fe 3+ ions. The paramagnetic centers produced by γ - irradiation of natural sepiolite minerals were attributed to the ĊH 3 at room temperature and ṠO − 2 and ṠO − 3 radicals at 113 K. These centers were found to be perfectly observable above 20 mW microwave power. The g values of all paramagnetic centers have been measured and the A values of some of them have been reported. The results were consistent with the literature data for similar paramagnetic centers.
Sepiolite
Microwave power
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Paramagnetism and diamagnetism of a material characterized by its magnetic susceptibility. When a material is exposed to an external magnetic field, magnetic susceptibility is defined as the ratio of the induced magnetization and the magnetic field. A paramagnetic material has magnetic susceptibility with positive sign. On the other hand, a diamagnetic material has magnetic susceptibility with negative sign. Atomically, paramagnetic materials consist of atoms that has orbital with unpaired electrons. Theoretical study of paramagnetic susceptibility and diamagnetic susceptibility are well described by Pauli paramagnetism and Landau diamagnetism, respectively. Although paramagnetism and diamagnetism are among the simplest magnetic properties of material that are studied in basic physics, theoretical derivations of Pauli paramagnetic and Landau diamagnetic susceptibility require second quantization formalism of quantum mechanics. We aim to discuss the paramagnetic and diamagnetic susceptibilities for simple three-dimensional quantum well using first quantization formalism.
Diamagnetism
Pauli exclusion principle
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