Specific heat and magnetic properties of single-crystalline ZnxDyyCrzSe4 spinels

The crystal structure, magnetic isotherm, magnetic susceptibility, electrical conductivity and specific heat measurements for single-crystalline ZnxDyyCrzSe4 (where x+y+z≈3) spinels are presented. A semiconducting behavior with the activation energy of 0.53 eV, an antiferromagnetic order with a Néel temperature TN=22 K and a strong ferromagnetic exchange evidenced by a positive Curie-Weiss temperature θ=79, 71 and 70 K with increasing Dy-content in the sequence 0.05, 0.13 and 0.19 were established. Below TN the magnetic field dependence of magnetization, M(H), shows two peaks at critical fields Hc1 and Hc2. The values of Hc1 decrease slightly with temperature, especially for the larger Dy-content, while the values of Hc2 drop rapidly with temperature. The magnetic contribution to the specific heat displays a sharp peak at TN, which is strongly shifted to much lower temperatures in the applied magnetic fields. Similar behavior was found for the temperature dependence of the specific heat C(T) plotted as C(T)/T vs. T. The value of the magnetic and phonon contribution to the entropy at TN and at H=0 is only ∼4.8, ∼4.4 and ∼4.2 J mol−1 K−1/Cr3+ for y=0.05, 0.13 and 0.19, respectively, much lower than the average magnetic contribution Sm=(z/2)Rln(2S+1)=12.33 J mol−1 K−1/Cr3+ calculated for Cr3+ ion with S=3/2, as the dysprosium one is paramagnetic.