Resonant x-ray magnetic scattering from alloys

We have studied (Formula presented) alloys with (Formula presented) 0.5, and 1.0 using resonant x-ray magnetic scattering. For the (Formula presented) neptunium compound we have confirmed previous neutron scattering results, but with much higher count rates and improved q resolution. Using the element specificity of the method, we have found that the temperature dependence of the uranium and the neptunium moments differ in the mixed (Formula presented) solid solutions and we present some tentative explanations for this behavior. In principle, by measuring the responses at the individual M edges we are able to determine the ratio of the magnetic moments on the two magnetic species in the random alloys. The observed variation of intensity versus energy is compared to a calculation of a (Formula presented) alloy using a localized model and a coherent superposition of (Formula presented) and (Formula presented) ions. The agreement between theory and experiment is reasonable, suggesting a ratio (Formula presented) in this alloy. Since (Formula presented) is known to be (Formula presented) for (Formula presented) the uranium moment is (Formula presented) This is much larger than (Formula presented) known to exist in (Formula presented) The increase is a consequence of the molecular field of the ordered (Formula presented) moments and is consistent with the crystal-field model proposed for the (Formula presented) ground state. © 2000 The American Physical Society.