Electron Paramagnetic Resonance Of Cr3 Research Articles

Electron Paramagnetic Resonance of Cr3+ Ions in ABO3 (A = Sc, In, Ga) Diamagnetic Crystals

A magnetic resonance method is applied to the investigation of a number of isostructural diamagnetic compounds ABO3 (A = Sc, In, and Ga) with small additions of Cr3+ ions (S = 3/2) sufficient to observe single-ion and pair spectra. It is shown that the resonance spectra for isolated Cr3+ ions can be described to a good accuracy by the ordinary axial spin Hamiltonian for 3d ions in octahedral oxygen environment. The parameters of the spin Hamiltonian are determined for single Cr3+ ion and Cr3+–Cr3+ pair. Lattice distorsions of the parent ABO3 crystals caused by the Cr3+ impurities is discussed.

Electron paramagnetic resonance of Cr3+ ions in ABO3 (A = Sc, Lu, In) diamagnetic crystals

A magnetic resonance method is applied to the investigation of a number of isostructural diamagnetic compounds ABO3 (A = Sc, Lu, In) with small additions of Cr3+ ions (S = 3/2) sufficient to observe single-ion spectra. It is shown that the resonance spectra for isolated Cr3+ ions can be described to a good accuracy by the ordinary axial spin Hamiltonian for 3d ions in octahedral oxygen environment. The parameters of the spin Hamiltonian are determined. It is established that Cr3+ ions in these crystals are characterized by easy-axis-type anisotropy.

Electron paramagnetic resonance of Cr3+ in near-stoichiometric LiTaO3

Electron-paramagnetic-resonance (EPR) experiments on the dominant Cr3+ center in near-stoichiometric LiTaO3 crystals, grown by the double crucible Czochralski method, are reported. A near complete roadmap of EPR positions was obtained allowing an accurate determination of the spin-Hamiltonian parameters. Newman superposition model calculations of zero-field splitting term were performed and support the model of Cr3+ incorporation within the Li octahedron. Calculations were also made for Cr3+ in LiNbO3, again good agreement with a Li site model was obtained for the main EPR center. The temperature dependence of the zero-field splitting parameter for Cr3+ in LiTaO3 was found to show anomalous behavior in the region of 40 K, suggesting the presence local structural instability at the ion site.

Field-swept pulsed electron paramagnetic resonance ofCr3+-doped ZBLAN fluoride glass

Field-swept pulsed electron paramagnetic resonance (EPR) spectraof a ZBLAN fluoride glass doped with a low concentration of Cr3+ areobtained using echo-detected EPR and hole-burning free induction decaydetection. We review the utility of the pulsed EPR technique in generatingfield-swept EPR spectra, as well as some of the distorting effects thatare peculiar to the pulsed detection method. The application of thistechnique to Cr3+-doped ZBLAN reveals that much of the broadresonance extending from geff = 5.1 to geff = 1.97,characteristic of X-band continuous wave EPR of Cr3+ in glasses, isabsent. We attribute this largely to the variation in nutation frequenciesacross the spectrum that result from sites possessing large fine structureinteractions. The description of the spin dynamics of such sites iscomplicated and we discuss some possible approaches to the simulation ofthe pulsed EPR spectra.

The mechanism of the phase transition in (CH3)2NH2A1(SO4)2·6H2O studied by EPR of Cr3+

The electron paramagnetic resonance (EPR) spectra of Cr3+ impurity in the ferroic (CH3)2NH2A1(SO4)2·6H2O monocrystals have been studied in the 80-400 K temperature range with an X-band spectrometer. The spin-Hamiltonian parameters determined at RT are: D=0.0923 cm-1, E=-0.0070cm-1, gx=1.9736, gy=1.9749 and gz=1.9715. Temperature dependence measurements of these parameters give useful information about the water molecule behaviour. The ferroelectric phase transition (PT) at Tc=152 K is most probably evoked indirectly by slowing down of rotation and reorientation of the H2O units. A model of the PT is proposed.

Off-axis extra lines in powder pattern electron paramagnetic resonance of Cr3+ in YAlO3

Powder sample electron paramagnetic resonance (EPR) spectrum of Cr3+ ions in YAlO3 crystals contains off-axis extra lines, which do not belong to the principal X, Y,and Z components of the fine structure. Orientation dependence of the EPR spectrum of Cr3+ doped YAlO3 single crystal confirms the existence of extra turning points corresponding to directions lying off the X, Y, and Z axes, consistent with theoretical predictions. This results in five EPR lines due to the transition between the central Kramers doublet in the powder system. The observed powder pattern EPR has been used in identification of Cr3+ as an impurity ion in undoped YAlO3 crystals.

Studies of chromium-doped sodium ammonium sulphate dihydrate: I. Electron paramagnetic resonance of Cr3+

Electron paramagnetic resonance (EPR) Of Cr3+ ions has been observed in single crystals of sodium ammonium sulphate dihydrate (SASD) doped with chromium. At 300 K the spectrum is relatively simple, exhibiting two main different sites, labelled alpha and beta . The spin-Hamiltonian parameters for these sites have been measured. The relative concentration of different paramagnetic sites shows marked sensitivity to unknown factors in the crystal growth. On lowering the temperature the spectrum becomes very complex, making detailed study of the various sites, and changes at any phase transition, impossible to elucidate. None of the spectra shows a marked change at the ferroelectric transition temperature, Tc=92 K.

Phase transitions in ferroelastic RbIn(MoO4)2 crystals by electron paramagnetic resonance of Cr3+ ions

EPR investigations of the cr3+ ion in trigonal double molybdate RbIn(MoO4)2 are reported. The spin Hamiltonian parameters of the Cr3+ complexes are: g∥ = 1.9640, g| = 1.9680, |D| = = 0.5400 cm−1 at room temperature. Two structural phase transitions are observed by changes in the EPR spectra of the Cr3+ ion. The spin Hamiltonian parameters of the Cr3+ complexes in the ferroelastic phase are reported. A structural distortion model of the high-temperature phase is suggested. This model is based on the motion of the oxygen atoms of the anion (MoO4)2-, constituting the environment of In3+. Below T1 = 163 K the distortion leads to a monoclinic phase with the space group symmetry C2/c. [Russian Text Ignored].

Electron paramagnetic resonance of Cr3+ in guanidinium aluminum sulfate hexahydrate

Electron paramagnetic resonance of Cr3+ in guanidinium aluminum sulfate hexahydrate

Electron paramagnetic resonance studies and linewidth anomaly of Cr3 in some ferroelectric alums

Electron paramagnetic resonance of Cr3+ in CH3NH3Ga(SO4)2 · 12H2O and CH3NH3Al(SeO4)2 · 12H2O (which are known to be ferroelectric) as a function of temperature and orientation has been studied. As one approaches Tc, an anomalous increase of resonance linewidth, which is very pronounced for the satellite transitions has been observed. It is observed experimentally that ΔHc ∼ (T - Tc)-n, where n ∼ 0.4 for temperatures near to Tc and n ∼ 2.0 for temperatures further from Tc. The EPR spectrum has also been observed in the ferroelectric phase. It is inferred that the water molecules in the immediate environment of the trivalent metal ion may be playing an important role in the mechanism of ferroelectricity in alums.