Element-specific magnetic order and competing interactions in Gd 0.8 Eu 0.2 S

We report on the determination of element-specific magnetic order for a Gd0.8Eu0.2S mixed crystal by means of X-ray resonance exchange scattering. For the first time, a different temperature dependence of the sublattice magnetization of two lanthanide ions was observed. With model calculations we were able to reproduce the measured temperature dependence of the reduced sublattice magnetization. We can show that competing magnetic interactions lead to the observed effects and can reveal the frustration mechanism.