Element-specific magnetic long- and short-range order and competing interactions in GdxEu1-xS

We report on an investigation of the magnetic properties of GdxEu1-xS mixed crystals with compositions in the range of 0.6 < x < 1. For the two samples Gd0.8Eu0.2S and Gd0.73Eu0.27S a long-range antiferromagnetic order was observed at low temperatures. Element-specific measurements exhibited a different temperature dependence of the reduced sublattice magnetisation of the two magnetic species. A model calculation and Monte Carlo simulations revealed that the different temperature dependence is due to frustration effects. These frustration effects lead to a break-down of the long-range order for higher europium contents. For the Gd0.67Eu0.33S-sample we were able to observe a short-range antiferromagnetic order with correlation lengths of a few 10 Angstrom with X-ray resonance exchange scattering