Magnetic X-ray Scattering from Cuprates*

Magnetic x-ray scattering studies of ordered spin-$\frac12$ copper moments in cuprates have been difficult to perform. While resonant scattering has been studied in one sample of Pr-barium cuprate ({\it PRB} {\bf 61}, 1251 (2000)), a direct observation of non-resonant scattering from cuprates ({\it e.g.} YBa$_2$Cu$_3$O$_{6+x}$, YBCO) has not been made. We have succeeded in observing non-resonant magnetic scattering of x- rays from antiferromagnetically ordered YBCO insulators. Magnetic Bragg peaks characterized by ($\frac12$, $\frac12$, 0) were found to be resolution limited in all directions revealing correlation lengths of $\sim$1000 A. By using a polarization analyzer to exactly suppress charge scattering we were able to obtain a peak-to-background ratio of $\sim$7 with a peak count rate of 2- 3 counts/second. Q-dependence of the intensities is consistent with the known structure and scattering cross section. Our study demonstrates the feasibility of such a technique at a third generation synchrotron source, which can be used for studying very small samples.