Single-crystal magnetic susceptibilities of TbRh2Si2. Determination of anisotropic exchange parameters

Magnetic susceptibilities are measured parallel and perpendicular to the unique axis of a single crystal of tetragonal TbRh2Si2 (14/mmm). Curie-Weiss behavior is observed in the temperature range 200–300 K for both orientations of the magnetic field, with the parameters: Xc(T): Cc = 13.25 K cm3 mol−1 (μeff = 10.3 μB/Tb3+), Θc = 50(5) K, and Xa(T): Ca = 13.7 K cm3mol−1 (μeff = 10.3, μB/Tb3+),gQa = −70(5) K. Using the general approach of Boutron specialized to the Tb site symmetry of D4h, the Weiss constants are related to exchange and crystal-field parameters as: Θ∥c = − J(J + 1)3 kJ̃exc + (2J − 1)(2J + 3)10 k B2∘, and Θ∥a = − J(J + 1)3 kJ̃exa − (2J − 1)(2J + 3)30 k B2∘ As B2∘ is known from Mössbauer spectroscopy data (155Gd in TbRh2Si2) the anisotropic exchange constants can be obtained as follows: Jexck = −9(2) K and Jexak = + 8(2) K. These results are qualitatively consistent with the known magnetic structure, which consists of ferromagnetic sheets normal to the c-direction and coupled antiferromagnetically with the moments parallel to c. Measurements to 4.2 K disclose a TN value of 94(2) K, in agreement with previous work, but do not show any anomaly at lower temperatures as reported for powder samples.