Preparation and Properties of a High-Entropy Wolframite-Type Antiferromagnet, (Mn_0.2Co_0.2Ni_0.2Cu_0.2Cd_0.2)WO₄

The homogeneous high-entropy wolframite-type solid solution (Mn_1/5Co_1/5Ni_1/5Cu_1/5Cd_1/5)WO₄ was prepared by solid-state reaction at 1000 °C. Elongated "crystals" were grown from the Na₂WO₄ flux, but their strongly broadened powder X-ray diffraction patterns indicated partial dissolution. Nevertheless, successive annealing of the homogeneous solid solution for 3-4 h at 800, 700, and 600 °C did not bring any sign of dissolution. Thus, the material is kinetically stable at low temperatures although thermodynamically unstable. The long-range antiferromagnetic order was established at T_N ∼ 24.8 K. Based on magnetization and specific heat measurements, a magnetic phase diagram was built, demonstrating the presence of an additional field-induced phase. In contrast to the parent MnWO₄, no dielectric anomaly has been found down to 2 K.