Physical and Magnetocaloric Properties of TbPdAl₂ and the Ferromagnetic Solid Solution Tb_1–xLu_xPdAl₂ (x = 0.1–0.9)

Abstract

TbPdAl 2 and the solid solution Tb 1−x Lu x PdAl 2 (x = 0.1−1) have been synthesized via arc-melting techniques using the elements as starting materials and crystallize in the orthorhombic MgCuAl 2 -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. TbPdAl 2 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 ∼ T 2 behavior is evident. In the solid solution Tb 1−x Lu x PdAl 2 (x = 0−1), the ferromagnetic Curie temperatures decrease in a linear fashion with increasing Lu content. Investigations of the magnetocaloric properties of TbPdAl 2 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 TbPdAl 2 , therefore, also exhibits comparably low values of 32, 81, 142, and 178 J kg −1 .

Excellent cryogenic magnetocaloric properties in heavy rare-earth based HRENiGa2 (HRE = Dy, Ho, or Er) compounds

“…This is due to the large total orbital quantum numbers (J) of HRE elements, which lead to large magnetic moments that are beneficial to the magnetocaloric properties. Recently, ternary intermetallic compounds, HRE-TM-X (X = p-block elements) with the stoichiometric ratio of 1:1:2, have received extensive attention for their diverse crystal structure and unique magnetic properties [34][35][36][37][38][39][40][41][42][43][44][45][46][47]. Their magnetic phase transition and magnetocaloric properties can be varied depending on the TM and p-block elements.…”