THE FIRST MEASUREMENTS OF A PURE MAGNETIC POWDER REFLECTION WITH X-RAYS. R J Cernik, S P Collins, D Laundy and C C Tang, Synchrotron Department, Daresbury Laboratory, Warrington, Cheshire, WA4 4AD, UK

We report the first successful measurements of magnetic x-ray powder diffraction from an antiferromagnet, performed at the uranium M4 edge in UO2. For some time, magnetic x-ray diffraction measurements on antiferromagnetic crystals have utilised the huge M-edge resonant enhancements to good effect, routinely providing intensities and resolution superior to those more traditionally associated with neutron scattering [1]. However, competition between the relatively weak Bragg intensities, and a combination of diffuse scattering and strong fluorescence signals has made powder measurements difficult.

Our experiment [2], carried out on SRS station 8.4, was configured for maximum count-rates and low background. The resulting (102) magnetic diffraction intensity was found to vanish above the magnetic ordering temperature and exhibit the anticipated resonance response. Moreover, the integrated intensity agreed remarkably well with a simple calculation of the magnetic cross-section.

We anticipate that measurements performed with high flux insertion devices on third-generation synchrotrons, such as the ESRF, should provide data of extremely high quality, and could be extended to less pronounced magnetic resonances, such as the L-edges of magnetic lanthanide compounds.

References

[1] McWhan D B, Vettier C, Isaacs E D, Ice G E, Siddons D P, Hastings J B,

Peters C and Vogt O Phys.Rev.B 42 6007 (1990)

[2] Collins S P, Laundy D, Tang C C and Cernik R J J.Phys.:Condens Matter

7 L223 (1995)