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 Jeff = 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 TN = 0.81 K. This family of Ba2RE2Ge4O13 compounds thereby provides a rare platform to investigate the novel spin ladder physics constructed by 4f electrons.