Polarized Dispersion of X-rays in Pyrite

Abstract

Diffraction of synchrotron radiation in a crystal of FeS 2 reveals dipolar anisotropy of anomalous scattering by Fe near its K-absorption edge, in spite of the almostregular octahedral geometry of the nearest S neighbors. At 7121 eV, the magnitude off changes with polarization direction by as much as 0.7 electron units. No effects of quadrupolar anisotropy were detected.

Polarization anisotropy of X-ray atomic factors and `forbidden' resonant reflections

“…Following a general theoretical treatment of the 'forbidden' reflections by Dmitrienko (1983Dmitrienko ( , 1984 and the first experimental verification, namely the observation of the excitement of 'forbidden' 00l ðl ¼ 2n þ 1Þ reflections in cubic NaBrO 3 (Templeton & Templeton, 1985a, 1986, similar effects have been found and studied in various other crystals like Cu 2 O , TiO 2 , MnF 2 , LiHSeO 3 (Kirfel & Petcov, 1992), Ba(BrO 3 ) 2 ÁH 2 O (Templeton & Templeton, 1992), Fe 3 O 4 (Kirfel et al, 1995a;Hagiwara et al, 1999;García et al, 2000;, FeS 2 (Nagano et al, 1996;Templeton & Templeton, 1997;Kokubun, Nagano et al, 1998), HoFe 2 (Collins et al, 2001); for further details see below. Such experiments are time consuming because once a resonance is detected the transition has to be proved and characterized by means of energy scans in steps of about 1 eV and numerous measurements at different polarizations and different settings in order to reveal the azimuthal variation of the 'forbidden' reflection's intensity in the often very disturbing presence of generally much larger multiple scattering effects.…”

“…So far, practically all resonant experiments have been done, with obvious experimental advantages and because other goals were aimed at, on extended sample faces being only partially illuminated by the beam. A few successful experiments on small crystals like that by Templeton & Templeton (1997) would make progress in the field.…”

“…Very similar 'forbidden' reflection spectra were found recently for pyrite-like CoS 2 and NiS 2 . Templeton & Templeton (1997) have studied the azimuthal profiles of 'forbidden' and weak allowed reflections from a small irregular sample (0:15 Â 0:19 Â 0:20 mm). The incident polarization was supposed to be completely r. The glide-plane 'forbidden' reflections 520 and 530 were measured for 7120.4 eV, and the absolute value jf k À f ?…”

Resonant1s→3dx-ray Bragg diffraction and structure factors for transition-metal compounds

“…[12][13][14] One might cite the factor sin 2 in Eq. ͑6.4͒ as evidence that the origin of the scattering is anisotropy in the orbital moments in the crystal axes, because the scattering vanishes should the principal axis coincide with either the a axis or the c axis.…”

“…This class of reflections include those called Templeton and Templeton scattering, [12][13][14] which arise from anisotropy in the moments referred to the crystallographic axes. We calculate the charge-forbidden structure factors for ͑paramagnetic͒ iron pyrite for which ͓111͔ is the principal axis of a resonant ͑iron͒ ion with site symmetry 3 (C 3i ).…”