Magnetic, thermal, and optical properties of single-crystalline CoTa₂O₆ and FeTa₂O₆ and their anisotropic magnetocaloric effect

The magnetic, thermal, and optical properties of single-crystalline CoTa₂O₆ and FeTa₂O₆ are reported. Optical dichroism was observed in CoTa₂O₆. Magnetic susceptibility χ(T) measurements reveal long-range antiferromagnetic order with Néel temperatures K and 8.11(5) K, respectively, and anisotropy in χ. The thermal expansion coefficients exhibit significant anisotropy and the influence of the magnetic ions and long-range order. A structural phase transition to orthorhombic occurs below T _N for FeTa₂O₆. Magnetic field H lowers T _N with its affect largest when H is directed along either [1 1 0] or [1  0], and smallest when directed along [0 0 1]. This leads to an anisotropic magnetocaloric effect that is investigated through measurements of the specific heat and magnetization in applied magnetic field. (paper)