Physical and Magnetocaloric Properties of TbPdAl₂ and the Ferromagnetic Solid Solution Tb_1-LuPdAl₂ (x = 0.1-0.9)

TbPdAl₂ and the solid solution Tb_1-LuPdAl₂ (x = 0.1-1) have been synthesized via arc-melting techniques using the elements as starting materials and crystallize in the orthorhombic MgCuAl₂-type structure (Cmcm). As expected, the unit cell volumes decrease due to the lanthanide contraction from the Tb to Lu compounds, thus showing Vegard behavior because of the differences of the ionic radii of the trivalent rare-earth cations. TbPdAl₂ orders ferromagnetically below T_C = 85.5(5) K and shows partial magnetic saturation already at low fields. The magnetic phase transition has been additionally investigated by heat capacity measurements, showing a broadened λ anomaly at T_HC = 83.2(1) K. The electrical resistivity is almost linear above T_C, indicating dominant electron-phonon interactions. Below the ordering temperature, electron-spin wave scattering with a ρ ∼ T² behavior is evident. In the solid solution Tb_1-LuPdAl₂ (x = 0-1), the ferromagnetic Curie temperatures decrease in a linear fashion with increasing Lu content. Investigations of the magnetocaloric properties of TbPdAl₂ obtained a maximum magnetic entropy change of -ΔS_M^max = 1.2, 2.2, 3.1, and 3.6 J kg^-1 K^-1 for the field changes of ΔH = 10, 20, 50, and 70 kOe, respectively. The rather low values are caused by entropy losses due to hysteresis behavior. The relative cooling power for TbPdAl₂, therefore, also exhibits comparably low values of 32, 81, 142, and 178 J kg^-1.