Structure and Magnetic Properties of a Family of Two-Leg Spin Ladder Compounds Ba₂RE₂Ge₄O₁₃ (RE = Pr, Nd, and Gd-Ho)

Compared with the intensive investigation on 3d transition metal (TM)-based spin ladder compounds, less attention has been paid to the ones constructed by rare earth (RE) ions. Herein, we report a family of RE-based spin ladder compounds Ba₂RE₂Ge₄O₁₃ (RE = Pr, Nd, Gd-Ho) crystallized into a monoclinic structure with the space group C2/c. The RE ions are arranged on a two-leg spin ladder motif along the b-axis, where the rung and leg exchange interactions are bridged via RE-O-RE pathways and RE-O-Ge-O-RE routes, respectively. Moreover, the much shorter rung distance in RE₂O₁₂ dimer units than the leg distance suggests that Ba₂RE₂Ge₄O₁₃ compounds are strong-rung spin ladder systems. All of the synthesized Ba₂RE₂Ge₄O₁₃ (RE = Pr, Nd, Gd-Ho) compounds exhibit dominant antiferromagnetic (AFM) interactions and the absence of magnetic order down to 1.8 K. Among the family members, Ba₂Dy₂Ge₄O₁₃ can be described by J_eff = 1/2 Kramers doublet states, and the low-temperature specific heat indicates the coexistence of the spin-dimerized state with a broad maximum at ∼2.4 K and long-range AFM order with T_N = 0.81 K. This family of Ba₂RE₂Ge₄O₁₃ compounds thereby provides a rare platform to investigate the novel spin ladder physics constructed by 4f electrons.