Electron spin resonance linewidths of Cr3+ in magnesium oxide

Electron spin resonance linewidths of Cr³⁺ in single crystal MgO at 9 GHz and 35 GHz were examined experimentally and theoretically for a range of Cr³⁺ concentrations. In contrast to the behaviour expected from dipolar broadening the experimental peak-to-peak linewidth for the 1/2 to–1/2 transition, which had a value of about 0.5 mT at 293 K, was independent of both polar angle and concentration over the range from 800 p.p.m. Cr to 15 100 p.p.m. Cr. The calculated dipolar linewidths exceeded those observed by factors of over one hundred; the ratio of momentsM ₄ ^1/2 /M ₂ ^1/2 derived from the experimental data lay between 1.33 and 1.39 and the lineshapes were markedly Lorentzian. The data suggested that Cr³⁺ entered the lattice substitutionally, occupying magnesium sites, that the linewidths were determined by exchange narrowing over the whole concentration range examined and that the exchange energy, whose values lay between 4 GHz and 100 GHz, varied linearly with concentration.     

Electron spin resonance linewidths of Fe3+ in magnesium oxide

Electron spin resonance linewidths of Fe³⁺ in single crystal MgO at 9 GHz were examined experimentally and theoretically for a range of Fe³⁺ concentration. In contrast to the behaviour expected from dipolar broadening the experimental derivative peak-to-peak linewidth for the 1/2 ↔ −1/2 transition, about 0.6 mT at 77 K and a polar angle of 0°, was independent of concentration from 140 to 8500 ppm. The calculated dipolar linewidths greatly exceeded those observed and values of the ratio of moments M ₄ ^1/4 /M ₂ ^1/2 derived from the experimental data lay between 1.33 and 1.48. Optical examination, coupled with heat-treatment experiments, confirmed that the predominant valency state present was Fe³⁺. The data suggested that Fe³⁺ entered the lattice substitutionally, occupying magnesium sites, and that the linewidths were determined by exchange narrowing over the whole concentration range examined.     

Electron spin resonance of MO5+ in KTiOPO4

The ESR spectra from Mo⁵⁺ ions in KTiOPO₄ single crystal were studied at 77 K. The ESR spectra reveal two different types of paramagnetic centers, one due to Mo⁵⁺ which occupy the Ti(1) position in the crystal and the other, due to Ti³⁺, formed at position Ti(2) in the crystal. The principal values and direction cosines of the g tensor are reported for the former center.     

Clustering and electron spin resonance linewidths in Fe/MgO

Electron spin resonance linewidths and integrated intensities for the 1/2 –1/2 transition of Fe³⁺ in cubic sites in single-crystal MgO have been examined at 9 GHz between 293 and 90 K for iron concentrations between 100 and 12 900 ppm. Very little of the iron is present in cubic sites as isolated Fe³⁺ ions. It is suggested that this is partly caused by clustering, even at extremely low concentrations. The measured linewidths, which agree well with those reported previously, have been analysed in terms of Kittel and Abrahams' dipolar broadening theory. The highest measured Fe³⁺ concentrations give linewidths comparable with those predicted, but for most samples the measured linewidths are considerably broader than those calculated. This broadening may be caused by interactions with the undetected iron, which accounts for the major fraction. There is no evidence for exchange narrowing of the Fe³⁺ lines for the range of concentrations examined.     

Electron spin resonance spectra of Gd3+ ions in K2SO4-ZnSO4 glasses

Electron spin resonance (ESR) spectra of Gd³⁺ ions doped in K₂SO₄-ZnSO₄ glasses have been studied on an X-band ESR spectrometer at different temperatures (–120 to 150 C). The ESR spectrum at room temperature exhibits three prominent features with effectiveg-values of 5.6, 2.83 and 2.02. The spectra are similar to the U spectra familiar in many oxide and fluoride glasses, indicating very low and disordered site symmetries with a broad distribution of crystal fields. Remarkable changes have been observed in the spectrum with changes in the temperature, concentration and glass composition. The broadening of theg 2.02 line with increasing Gd³⁺ ion content indicates that the dipole-dipole interaction between the resonant centres increases with increase in Gd³⁺ ion content. A weak band at 36350cm^–1 is observed in the optical absorption spectrum of 0.5mol% Gd³⁺ in K₂SO₄-ZnSO₄ glass which has been assigned to the transition⁸S_7/2⁶P_7/2.     

Electron spin resonance of FeVO4

We report on electron spin resonance (ESR) investigations of a FeVO₄ single crystal. Temperature and angular dependences of ESR resonance positions were measured and calculated in temperature range of 35–100 K. The spectra show rich angular dependences of the linewidth, the shape and the resonance field. They consist of a single broad line with asymmetric distortion. Due to the low symmetry of the crystal lattice this distortion can be explained by taking into account the influence of non diagonal dynamic susceptibility.     

Electron spin resonance and optical absorption spectra of Cu2+ ions in Na2SO4-ZnSO4 glasses

Electron spin resonance (ESR) and optical absorption spectra of Cu²⁺ ions in Na₂SO₄-ZnSO₄ glasses have been studied. The ESR spectra of Cu²⁺ ion-doped glasses exhibited a pronounced peak atg=2.07 and a shallow quadruplet atg=2.35, the latter arising from the hyperfine splitting of g. ESR spectra of Cu²⁺ ion-doped glasses were also studied by varying the concentration of Cu²⁺ions, temperature and composition of the glasses. The optical absorption spectra exhibited a broad absorption band in the near infrared region, which is attributed to²B_1g²B_2g transition. By correlating the ESR and optical absorption data, the bonding orbital coefficients ² and ₁ ² for Cu²⁺ ions have been evaluated.     

Electron paramagnetic resonance of Cu2+ and VO2+ ions in phosphate glasses

Electron spin resonance (ESR) spectra ofx(CuO · V₂O₅ (1 –x) (Na₂O · P₂O₅) andx(CuO · 2V₂O₅) (1 –x) (Na₂O · P₂O₅) glasses for 0 x 40 have been studied at the X-band and at 300 K. It is found that forx 5, both Cu²⁺ and VO²⁺ are present, mostly as isolated species. Forx 10, broad resonance lines atg = 2.1524 forx(CuO · V₂O₅) (1 –x) (Na₂O · P₂O₅) and atg = 2.1448 forx(CuO · 2V₂O₅) (1 –x) (Na₂O · P₂O₅) are observed which may be mainly due to dipole-dipole type interaction between transition metal (TM) ions. Spin Hamiltonian parameters of TM ions have been calculated. Optical spectra of the sodium phosphate glasses doped with single TM ions have also been studied. The theoretical optical basicity, A_th, of these doped glasses has been calculated. It is found that for VO²⁺ ionsg ,g and increase whileA ,P and g _|/g decrease with increase in A_th. However, no significant change is observed in the spin Hamiltonian parameters of Cu²⁺ with the change in A_th.     

Electron spin resonance in single crystal yttria stabilized zirconia

Electron spin resonance has been observed at 35 GHz in 8 and 12 mol % yttria stabilized zirconia single crystals before and after blackening by current passage. Measurements were made between 293 and 77K. In both as-grown and blackened crystals the spectra showed anisotropic lines (type A) characterized by g =2.003±0.002 and g =1.880 ±0.002 with respect to a [1 1 1] symmetry axis and a broader, slightly anisotropic line (type B) centred near g=1.993. In current blackened crystals a weak isotropic line (type C) was also found near g=1.986. The type A lines are attributed to a charged complex formed by an electron trapped at an oxygen vacancy and associated with an yttrium ion. Tentative models are suggested to explain the type-B and type-C lines.     

Electron spin resonance and electrical conductivity of vanadate glasses

Electron spin resonance (ESR) and d.c. conductivity were measured for a series of vanadium borophosphate glasses before and after heat treatment. The ESR spectra showed the presence of vanadium in the V⁴⁺ state in all untreated and heat-treated samples free from iron. The variable temperature ESR and d.c. conductivity results obtained on the sample free from iron showed an inflexion at about 140°C. The electrical conductivity was found to decrease on substitution of 1 mol.% V₂O₅ by 1 mol.% Fe₂O₃ which may be due to a decrease in the V⁴⁺/V ratio. However, the electrical conductivity was found to increase on addition of more than 1 mol.% Fe₂O₃ which may be due to possible hopping conduction between Fe²⁺−Fe³⁺, V⁴⁺−Fe³⁺ and Fe²⁺−V⁵⁺. The increase in conductivity in the sample heat treated at 350°C relative to those heat treated at 300°C and 400°C may be due to the variation in the V⁴⁺/V total ratio. The activation energy values for untreated and heat-treated samples were calculated and were found to depend on the variation in the V⁴⁺/V ratio and the microstructure.     

Electron spin resonance of Gd3+ in ceramic PbTio3

The electron spin resonance spectra of Gd³⁺ in ceramic PbTiO₃ and, as a comparison, in powdered Bi₃Mg₂(NO₃)₁₂·24H₂O are reported. The interpretation, in terms of crystal field parameters, of the spectrum of the double nitrate is in good agreement with previous single crystal results. It was not possible to interpret the room temperature spectrum of PbTiO₃. However, the spectrum of this compound measured above its Curie-temperature (～763 K) can be interpreted. This shows that the local crystal field symmetry of a small part of the Gd³⁺-ions at this temperature is orthorhombic or lower, not-withstanding the cubic lattice symmetry of PbTiO₃ under these conditions.     

Electron spin resonance study of amorphous hydrogenated carbon films

Amorphous hydrogenated carbon films of high electrical resistivity were studied using electron spin resonance (ESR) both as prepared and after vacuum heat treatment. The films were produced by deposition from a d.c. magnetron glow discharge containing acetylene. In the as-prepared state, all films gave a composite ESR signal with a broad and a narrow component suggesting the presence of two distinct phases. When the films were annealed, an intense narrow signal was produced which had the same temperature dependence of the signal intensity and the linewidth as that reported in the literature for heated carbonaceous material. By analogy with published work on the heating of carbonaceous material, a model of the structure is proposed based on threefold coordinated graphitic sheets formed by fusion of aromatic rings. Calculations of the average molecular weight of the graphitic sheets are given for two annealing temperatures.     

Electron spin resonance and electrical properties of co-evaporated SiO/SnO2 thin films

Electron spin resonance (ESR) measurements are reported for various compositions of SiO/SnO₂ thin films and indicate a decrease in the value of spin density for increasing SnO₂ content in the SiO. Annealing of the device further reduces the value of the spin density. The electrical activation energy and resistivity have been found to increase after annealing of the device and the results are compared with the optical and ESR measurements.