Electron paramagnetic resonance of Fe3+ in orthorhombic KNbO3

EPR spectra of KNbO₃:Fe single crystals are obtained in the - 10–110°C temperature range. The angular dependence of resonant lines is well reproduced by spin Hamiltonian parameters relevant to a Fe³⁺ impurity ion substituted to Nb ion in KNbO₃ crystal. The temperature behaviour of resonant lines is explained by a quadratic dependence of axial parameter D vs polarization P_s of the form D = βP²_s in the orthorhombic phase.     

Electron paramagnetic resonance of Gd3+ in PbTe

X-band EPR measurements have been made on single crystals of lead telluride doped with gadolinium in nominal concentrations of 0.04, 0.1, 0.5, and 1.0 atomic %. Fully resolved fine structure appropriate to Gd³⁺ ions in sites of cubic symmetry was observed in the temperature range from 4.2 K to 300 K. The parameters of the spin Hamiltonian were determined from the spectra by diagonalization of the Hamiltonian matrix and the use of a nonlinear least-squares program. The three parameters are independent of concentration and at 4.2 K have the values g=1.9908 ± 0.0002, b₄= ?110.16 ± 0.08 MHz and b₆ = +2.40 ± 0.02 MHz respectively. The parameter b₄ is temperature dependent; the other parameters are not, to within experimental accuracy. An additional resonance line, possibly analogous to the “cluster” line observed in metallic systems, was seen near g=2.     

ESR of Fe3+ -Rhombic,Fe2+ -Vo and Fe1+ -Vo complexes in SrTiO3

Three new Fe-defect complexes have been identified by ESR in Fe doped crystals of SrTiO₃. These are an Fe³⁺ center with rhombic fine structure in the “as-grown” crystals, and the vacancy associated complexes Fe²⁺ -V_o and Fe¹⁺ -V_o in “reduced” crystals. Photo-excited charge transfer effects are observed for these centers.     

Electron paramagnetic resonance of 61Ni+ in CuGaS2

EPR of ⁶¹Ni⁺ doped CuGaS₂ at 4.2 K leads to the following experimental data: $\text{g = 1.918 ± 0.006 A  < 12 × 10}{}^{-4}\text{cm}{}^{-1}\text{, g}{}_{\mathrm{\perp }}\text{= 2.328±0.006 A}{}_{\mathrm{\perp }}\text{= (65±2) × 10}{}^{-4}\text{cm}{}^{-1}$. High axial field splitting of ²T₂ state stabilizes the center against Jahn-Teller interaction. Covalency reduction factor k is 0.76.     

Electron paramagnetic resonance parameters and local structure for Gd3+ in KY3F10

The electron paramagnetic resonance parameters, zero-field splittings (ZFSs) b₂⁰, b₄⁰, b₄⁴, b₆⁰, b₆⁴ and the g factors for Gd³⁺ on the tetragonal Y³⁺ site in KY₃F₁₀ are theoretically studied from the superposition model for the ZFSs and the approximation formula for the g factor containing the admixture of the ground ⁸S_7/2 and the excited ⁶L_7/2 (L=P, D, F, G) states via the spin-orbit coupling interactions, respectively. By analysing the above ZFSs, the local structure information for the impurity Gd³⁺ is obtained, i.e., the impurity-ligand bonding angles related to the four-fold (C₄) axis for the impurity Gd³⁺ center are found to be about 0.6° larger than those for the host Y³⁺ site in KY₃F₁₀. The calculated ZFSs based on the above angular distortion as well as the g factors are in reasonable agreement with the observed values. The present studies on the ZFSs and the local structure would be helpful to understand the optical and magnetic properties of this material with Gd dopants.      

Electron spin resonance investigation of the substitution of Fe3^＋ for Ti4^＋ ions in rutile TiO2 single crystal

A Fe doped rutile TiO 2 single crystal is grown in an O 2 atmosphere by the floating zone technique.Electron spin resonance (ESR) spectra clearly demonstrate that Fe 3+ ions are substituted for the Ti 4+ ions in the rutile TiO 2 matrix.Magnetization measurements reveal that the Fe:TiO 2 crystal shows paramagnetic behaviour in a temperature range from 5 K to 350 K.The Fe 3+ ions possess weak magnetic anisotropy with an easy axis along the c axis.The annealed Fe:TiO 2 crystal shows spin-glass-like behaviours due to the aggregation of the ferromagnetic clusters.     

Identification of Fe4+ and Fe5+ charge-transfer photochromic absorption bands in SrTiO3

Optical absorption and the enhancement and bleaching of Fe³⁺ and Fe⁵⁺ electron paramagnetic resonance in SrTiO₃: Al measured as a function of wavelength and time show that the photochromic absorption bands are due to electron transfer from O^2- valence states to Fe⁴⁺ and Fe⁵⁺. They occur at 2.09 and 2.82 eV for Fe⁴⁺ and at 1.99 and 2.53 eV for Fe⁵⁺.     

Electron paramagnetic resonance of Gd3 in YCl3·6H2O

The electron paramagnetic resonance spectrum of Gd³⁺ in YCl₃·6H₂0 with $\text{1}\text{100}$ dilution of Gd/Y ions, has been studied with an X-band spectrometer at 295, 77 and 1.77°K and with a K-band spectrometer at 295 and 77°K. The individual values of all the parameters are evaluated from the data at the three temperatures. In particular, the following values for the g-tensor and the zero-field splitting parameters b₂⁰ and b₂² are obtained from X-band data: at 295°K, g_zz = 1.994±0.005, g_xx = 1.992±0.005, g_yy = 1.997±0.005, b₂⁰ = 1.898 ±0.015 GHz, b₂² = ?2.247 ± 0.015GHz; at 77°K, g_zz = 1.999±0.008, g_xx = 2.000±0.008, b₂⁰= 1.978 ±0.022 GHz, b₂² = ?1.574±0.022GHz; at 1.77°K, g_zz = 2.002±0.010, g_xx = 1.990 ±0.010, b₂⁰ = 2.011 ± 0.025 GHz, b₂² = ?1.650 ±0.025 GHz. (The K-band values are found to be consistent with the X-band values). From the angular dependence of the data in the ZX plane (i) the angle X₀ which the Z axis makes with the a vector of the unit cell, is determined to be 58.00 ±0.25° and (ii) the existence of pseudo-symmetry axes at ±5° from the Z axis in the ZX plane as found by heat capacity and specific heat data has been confirmed. An estimate is also made of the extent of admixture of the excited ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ state with the ground state ${}^8\text{S}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$.     

Electron spin resonance and optical identification of Fe4+-V0 in SrTiO3

The electron spin resonance of the minority defect Fe⁴⁺-V₀ has been observed in SrTiO₃. It is the first pair center identified with a two-fold positive charge with respect to the lattice. For Fe⁴⁺ it occurs in the unusual high spin S = 2 state. Optically-induced conversion to the neighbor Fe³⁺-V₀ charge state served to identify the acceptor transfer bands, showing the potentiality of the conversion-rate method.     

Electron impact excitation of Fe25+

A three-state close-coupling calculation of the impact excitation of the 2s and 2p states of the hydrogenic ion Fe²⁵⁺ has been performed using the algebraic variational method.     

Electron paramagnetic resonance of Re4+ : (NH4)2 PtCl6

The electron paramagnetic resonance of Re⁴⁺ in single crystals of (NH₄)₂PtCl₆ at frequencies near 10 GHz is reported. The results are interpreted in terms of two types of centre, one with octahedral symmetry and the other with an axial distortion along a trigonal axis. It is suggested that this distortion could be due to variations in the orientations of the ammonium ions.     

Electron exchange between Fe2+ and Fe3+ ions on octahedral sites in spinels studied by means of paramagnetic Mössbauer spectra and susceptibility measurements

Mössbauer spectra were obtained of the paramagnetic spinels $\text{Zn}{}^{\mathrm{2+}}\text{|}\text{Zn}{}^{\mathrm{2+}}{}_{\mathrm{<mtext>(1?x)</mtext><mtext>2</mtext>}}\text{Ti}{}^{\mathrm{4+}}{}_{\mathrm{<mtext>(1+x)</mtext><mtext>2</mtext>}}\text{Fe}{}^{\mathrm{3+}}{}_{\mathrm{<mtext>(1?</mtext><mtext>x)</mtext>}}\text{Fe}{}^{\mathrm{2+}}{}_{\mathrm{x}}\text{|}\text{O}{}_4$ and susceptibilities were measured. The strong difference between the paramagnetic Fe²⁺ and Fe³⁺ spectrum, due to the different quadrupole splitting, is used for the distinction between the two species. At 300 K a superposition of the Fe³⁺ and the Fe²⁺ spectra is found for most of the iron and, in addition, some continuous absorption. The latter is strongest for equal Fe³⁺ and Fe²⁺ concentration $\text{(x =}\text{1}\text{2}\text{)}$ while it disappears towards the end members (Fe³⁺ only or Fe²⁺ only) as well as with decreasing temperature (between 78 and 200 K). From this it is concluded that it arises from thermally activated electron exchange, the frequency of which passes a “critical” value of ～10⁸ sec^?1 for increasing temperature. Paramagnetic susceptibilities are found to obey a Curie-Weiss law down to low temperatures. From the dependence of the asymptotic Curie temperature on the composition the magnetic interaction parameters J₁₁ = ?1.4 K, J₂₂ = ?3.3 K and J₁₂ = + 1.6 K for the Fe³⁺Fe³⁺, Fe²⁺Fe²⁺ and Fe³⁺Fe²⁺ interactions are derived. The experimental results are discussed in terms of a hopping model with an activation energy q ～- 0.12eV and a non-equivalence of the octahedral sites expressed by a varying potential energy difference U₀ between neighbouring sites. The continuous absorption at 300 K for $\text{x =}\text{1}\text{2}$ is attributed to about 17% of the iron on sites with U₀ running from 0 to ??0.06 eV. The ferromagnetic Fe³⁺, Fe²⁺ interaction (J₁₂) is attributed to electron transfer from localized Fe²⁺ ions to Fe³⁺ neighbours via a transfer integral b of the order of 0.05 eV. The magnitudes of J₁₂ and b are tentatively explained.     

Far infrared absorption of Fe2+ in KMgF3

Far infrared absorption in cubic KMgF₃ doped with Fe²⁺ is reported . A line is observed at 87cm^?1, which is assigned to the (Γ_5g → Γ_3g, Γ_4g) transition in the Fe²⁺. The reduction in the spin-orbit coupling from the free ion value has been predicted by Ham, Schwarz and O'Brien.     

Effects of Eu3+  Fe3+ exchange interaction on the spin Hamiltonian parameters of Fe3+ in EuGaG

The anisotropic exchange $\text{1}\text{3}\text{a}{}_{\mathrm{\mu \nu }}\text{Y}{}_{\mathrm{\mu \nu }}\text{(L}{}_{\mathrm{<mtext>Eu</mtext>}}\text{)S}{}_{\mathrm{<mtext>Eu</mtext>}}\text{· S}{}_{\mathrm{<mtext>Fe</mtext>}}\text{(0 < μ ? 6)}$ is incorporated with the isotropic exchange ?2 a₀₀S_Eu · S_Fe to interpret the observed spin-Hamiltonian parameters g and D of Fe³⁺ doped into EuGaG. Calculations from the observed g shifts yield a value of a₀₀ equal to 0.01 K. In order to explain the observed D shift, it is concluded that the spherical harmonics Y_μν(L_Eu) with μ > 2 are of dominant importance.     

Absorption spectra of Bi3+ and Fe3+ in Y3Ga5O12

The absorption spectra of Y₃Ga₅O₁₂:(Fe³⁺), Y₃Ga₅O₁₂:(Bi³⁺) and Y₃Ga₅O₁₂:(Bi³⁺, Fe³⁺) are presented to 40,000 cm^-1. Assignments are discussed and the transitions analysed in terms of their involvement in the large Faraday rotation observed in bismuth substituted iron garnets.     

Stabilization of Fe2+ centers in LiNbO3: Ti waveguides

Holographic measurements in LiNbO₃: Ti waveguides are reported indicating a mode dependent enhancement of photoconductivity. This enhancement can be explained by a stabilization of Fe²⁺ centers in the waveguide which are responsible for optical damage effects.     

The sign of Fe3+OCr3+ superexchange determined from Fe57 hyperfine field measurements

The sign of the super-transferred hyperfine field at an impurity site is shown to depend on the sign of the impurity-host superexchange interaction. This fact is used to determine that the Fe³⁺OCr³⁺ superexchange in YCrO₃ is antiferromagnetic.     

Estimation of 4s covalent bonding of Fe2+ and Fe3+ ions in NiO

The charge densities of the 4s electrons in Fe²⁺ and Fe³⁺ ions in the ionic compound, NiO, were measured from an internal conversion experiment and compared with some predicted values on the basis of different theoretical methods.     

Photolytic production of Fe3+ in CaS

Calcium sulfide powder containing iron as an impurity was irradiated with 580, 366 or 254 nm light at 77 K. Irradiation enhanced a broad (16 G peak-to-trough) electron paramagnetic resonance (EPR) signal at g = 2.017 and caused six sharp (～1 G) lines to appear in the X-band EPR spectrum at 347, 529, 956, 1963, 3547 and 5376 G. Enrichment of CaS with Fe²⁺ produced samples with similar photochemistry. It is proposed that irradiation causes the reaction Fe²⁺ + trap → Fe³⁺ + trap^?, whose products give rise to six sharp EPR lines assigned to Fe³⁺ and a broad line associated with trap^?. Both hyperfine splitting by ⁵⁷Fe (13 G) and superhyperfine splitting by ³³S (11.4 G) are observed in the six line spectrum. The environment of the photo-generated Fe³⁺ has less than octahedral symmetry. V²⁺ was observed at octahedral sites in unirradiated CaS for the first time, and is characterized by the EPR parameters g = 1.961 and A (hyperfine coupling) = 74.6 × 10^?4 cm^?1. EPR signals due to Mn²⁺ and Cr³⁺ at octahedral sites and Fe³⁺ at a low symmetry site were also observed in unirradiated CaS.     

ESR study of Fe3+ and Mn2+ ions on trigonal sites in ilmenite structure MgTiO3

Electron spin resonance has been observed for Fe³⁺ and Mn²⁺ ions occupying sites with trigonal symmetry in undoped and doped Verneuil-grown crystals of the ilmenite type compound MgTiO₃. At 300 K, the fine structure parameters in the spin Hamiltonian are (in 10^?4cm^?1) D = +844 (± 1), (a? F) = +118 (± 1), a = 69 (± 7) for Fe³⁺ and D = +164 (± 1), (a ? F) = +10.2 (± l), a = 7.0 (± 1) for Mn²⁺. These values are compared with literature data for Fe³⁺ and Mn²⁺ in other oxides, especially Al₂o₃, with particular reference to the recent “superposition” theory of the effect of a trigonal distortion. From the orientation of the axes of cubic pseudosymmetry of the spin Hamiltonian, and with the assumption that a has the same sign for both ions, it is proposed that Fe³⁺ and Mn²⁺ occupy the same octahedral site, namely the Mg²⁺ site. Anomalous line splittings observed for one sample were attributed to twinning on (0001) or {1120} planes.