Here we present the discovery and characterization of a series of antimonides ${Ln}_2{\mathrm{Ti}}_9{\mathrm{Sb}}_{11}$ (Ln: La–Nd) that exhibit well-isolated, $n=2$ rare-earth spin ladders. We discuss the structure of these compounds, with a particular focus on the magnetic Ln spin ladders. ${\mathrm{Nd}}_2{\mathrm{Ti}}_9{\mathrm{Sb}}_{11}$ and ${\mathrm{Ce}}_2{\mathrm{Ti}}_9{\mathrm{Sb}}_{11}$ exhibit antiferromagnetic interactions and a well-defined doublet ground state, whereas ${\mathrm{Pr}}_2{\mathrm{Ti}}_9{\mathrm{Sb}}_{11}$ exhibits a weakly magnetic singlet ground state. ${\mathrm{Nd}}_2{\mathrm{Ti}}_9{\mathrm{Sb}}_{11}$ is a poor metal with an electrical resistivity of $0.1\mathrm{m}\mathrm{\Omega }$ cm at 300 K and weak temperature dependence. The thermal conductivity along the ladder exhibits significant field dependence even at 40 K, considerably higher than the magnetic ordering temperature of 1.1 K. Compared to compounds with transition metal spin ladders, the rare-earth elements impart much lower energy scales, making these compounds highly tunable with external stimuli like magnetic fields. The diverse magnetism of the rare-earth ions and Ruderman-Kittel-Kasuya-Yosida interactions further contribute to the potential for a wide array of rich magnetic ground states, positioning these materials as a rare example of an inorganic square spin-ladder platform.

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• Crystal structure
• Magnetism
• Rare-earth magnetic materials
• Crystal growth
• Spin ladders
• X-ray diffraction