H. Rager

Electron spin resonance of trivalent chromium in forsterite, Mg2SiO4

AbstractThe electron spin resonance (ESR) spectrum of Cr3+ in a synthetic single crystal of forsterite doped with Cr2O3 was studied at room temperature in the X-band frequency range. The dependence of the observed spectra on the crystal orientation with respect to the applied magnetic field was investigated. The ESR spectra are described by the spin Hamiltonian

Electron paramagnetic resonance and polarized optical absorption spectra of Ni2+ in synthetic forsterite

H = \beta HgS + D(S_Z^{\text{2}} - {\text{1/3}}S{\text{(}}S{\text{ + 1)) + }}E{\text{(}}S_x^{\text{2}} - S_y^{\text{2}} {\text{)}}

Structure and phase transitions in Ca2CoSi2O7–Ca2ZnSi2O7 solid-solution crystals

with S=3/2. The spin resonance reveals that the chromium ions are located at both the M1 and M2 positions. Other possible substitutional or interstitial Cr3+ positions may be possible, but were not observed. The site occupancy numbers of Cr3+ at M1 and M2 are roughly 1.2×10−4 and 0.8×10−4, respectively, assuming that chromium is oxidized completely. The preference of the chromium ions for M1 was interpreted qualitatively in terms of crystal field criteria. The rhombic and axial spin Hamiltonian parameters, D and E, and the directions of the magnetic axes obtained for M1 and M2 are consistent with the respective oxygen coordination polyhedra.

Transition from the incommensurately modulated structure to the lock-in phase in Co-åkermanite

The electron paramagnetic resonance (EPR) spectrum of Cr3+ in synthetic crystals of forsterite consists primarily of lines of Cr3+ “isolated” at the M1 and M2 positions in a “perfect” crystal environment without local charge compensation. In addition it shows two nonequivalent superhyperfine-split sextets with different intensities which are due to strong interaction of the Cr3+ electron spin S (S=3/2) with an adjacent nuclear spin I(I=5/2). Electron nuclear double resonance (ENDOR) experiments revealed that the sextets result from Cr3+ (M1) - Al3+ and Cr3+ (M2) - Al3+ pairs, Al being located at adjacent tetrahedral Si sites. The g, D, A, and A′ tensor components of the Cr3+ - Al3+ pairs have been determined at room temperature. The values of the pairs are distinct although they are not very different from the corresponding data of “isolated” Cr3+. From the intensities of the EPR spectra the relative concentration of the Cr3+ - Al3+ pairs with respect to “isolated” Cr3+ has been estimated.

Spectroscopic study of natural gem quality “Imperial”-Topazes from Ouro Preto, Brazil

AbstractThe investigated Ni doped forsterite was grown with the floating zone technique. The EPR spectra were taken at room temperature using both 9.5 and 35 GHz. All specimens show EPR signals resulting from Mn2+ at M2 and Fe3+ at M1, M2, and Si positions. Ni2+ EPR signals are observed at 35 GHz but not at 9.5 GHz. The Ni2+ spectra are described by the spin Hamiltonian

Ti(III) in synthetic pyrope: A single-crystal electron paramagnetic resonance study

H = \beta SgB + D\left( {S_{\text{z}}^{\text{2}} - \left( {S + 1} \right)S/3} \right) + E\left( {S_{\text{x}}^{\text{2}} - S_{\text{y}}^{\text{2}} } \right)