Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

4C/2001G242

Resonant X-ray scattering from hematite, Fe2O3, below the Morin temperature
Jun KOKUBUN*, Shunsuke KAWAI, Ayako WATANABE and Kohtaro ISHIDA
Faculty of Science and Technology, Tokyo University of Science, Noda, Chiba 278-8510
Introduction
Hematite, α-Fe2O3, has a corundum structure with antiferromagnetic moments perpendicular to rhombohedral[111] axis at room temperature. At the Morin temperature(TM = 250 K) their directions change parallel to the [111].
Anisotropic resonant scattering from hematite was firstobserved by Finkelstein et al.[1] and they concluded thatthe observed azimuthal angle dependence is attributed toonly electronic quadrupole transitions.
We measured before the energy spectra of the 111 and333 forbidden reflections intensities near the Fe Kabsorption edge at room temperature. Both spectra
showed one peak in the pre-edge region and small nonresonant intensity. The azimuth dependence of the 111
and 333 reflections measured at the non-resonant energy
showed twofold symmetry. At the resonant energy, on theother hand, the 111 azimuth dependence showed
threefold pattern and that of the 333 reflection showed
complicated pattern.[2,3] In this report, we haveinvestigated the reflections below the Morin temperaturein order to explain the magnetic scattering contribution.
Experimental Results
The experiment was carried out with four-circle
diffractometers at BL4C, where the incident beam was σpolarized. The integrated intensities were measured forthe 111 and 333 forbidden reflections at different
temperature, X-ray energies or azimuthal angles aroundthe scattering vector.
Figure 1 shows the temperature dependence of the 111
forbidden reflection intensity at non-resonant energy. The
intensity is decreasing from the 250 K and almost
vanishes below the 200 K. This result indicates that themagnetic moments do not contribute to the reflection
below the Morin temperature because their directions
change. This property can be explained by non-resonant
magnetic scattering due to the antiferromagnetic structure.
Figure 2 shows the azimuthal angle dependence of the333 forbidden reflection at 150 K and the resonant peakenergy. This result shows obviously threefold symmetry
in contrast to the intricate pattern at room temperature.
The observed 333 azimuth dependence (dots) in Fig. 2
is in good agreement with the fitting curve based on theelectric dipole-quadrupole and quadrupole-quadrupole
scattering (solid line). The threefold pattern of the 111
azimuth dependence does not change below the Morintemperature and is also explained by these electrictransitions. These results indicate that the 333 reflection
at low temperature and the 111 reflection are caused byonly electric multipole transition process.

Moreover the resonant 333 reflection intensity at roomtemperature is much larger than that of the non-resonant
one. From these results we conclude that the complicatedazimuth dependence of the resonant 333 reflection isaffected by spin-dependent resonant magnetic scattering.

Fig. 1 Temperature dependence of the 111 forbidden
reflection at non-resonant energy.

Fig. 2 Azimuthal angle dependence of the 333 forbidden
reflection at 150 K and the resonant peak energy.
References[1] K. D. Finkelstein , Q. Shen and S. Shastri: Phys. Rev.
Lett. 69, 1992, 1612.
[2] A. Watanabe et al.: PF Act. Rep. 2000 #18B, 90.
[3] J. Kokubun et al.: PF Act. Rep. 2002 #20A, 21.
* kokubun@ph.noda.tus.ac.jp

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