Spin-glass properties of a concentrated system with ferromagnetic and antiferromagnetic interactions

The Eu1-xGdxS system goes from ferromagnetism for small x to antiferromagnetism for large x[1]. We have studied the specific heat and the magnetic properties of that system in the concentration range where the Curie-Weiss temperature, cursive-theta sign, changes sign. Both measurements clearly indicate a spin-glass freezing for x ∼ 0.5 and a mixed state for x ≳ 0.6. Ferromagnetic clusters have been observed in both the spin-glass and in the mixed regimes.