Specular Magnetic Reflectivity Measurements of UO_2

There is considerable interest in the application of X-ray scattering to the study of the magnetic structure near a surface. In our earlier work we reported the observation of magnetic truncation rods for an (001) surface of UO_2(G.M. Watson, D. Gibbs, G.H. Lander, B.D. Gaulin, L.E. Berman, Hj. Matzke, and W. Ellis, Phys. Rev. Lett. 77, 751 ('96).). We also found an enhanced magnetic disorder near the surface when the sample temperature was raised towards the bulk Neel temperature (T_N). In order to further characterize this disorder we have performed specular magnetic x-ray scattering measurements as a function of temperature utilizing a polarization analyzer to remove the specular charge scattering. These results indicate that the width of the magnetic interface diverges as the temperature approaches T_N. Work at Brookhaven National Laboratory is supported by the U.S. DOE under contract No. DE-AC02-CH7600016.