A family of rare-earth diamond chain compounds NaB a 3 R E 3 S i 6 O 20 ( R E = Nd , Gd-Dy): Synthesis and magnetic characterization

The quasi-one-dimensional diamond spin chain systems have attracted significant research attention for unveiling novel quantum magnetic phenomena driven by low dimensionality and magnetic frustration. Even though several $3d$ transition-metal (TM)-based diamond chain magnets have been studied, rare-earth (RE) counterparts are still rare. Herein, we report a family of rare-earth diamond chain compounds, NaBa₃RE₃Si₆O₂₀ (RE=Nd, Gd-Dy), which crystallize in an orthorhombic structure with the Ama2 space group. The structural analysis reveals that the edge-sharing REO₈/REO₇ polyhedra form an infinite diamond chain along the c axis with well separation by the nonmagnetic SiO₄ tetrahedra and BaO₇/BaO₈ polyhedra perpendicular to the c-axis, in which the nearest neighboring (NN) intra-chain RE-RE distance dᵢₙₜᵣₐ~3.818-3.9160.16em0ex is significantly shorter than the NN inter-chain distance dᵢₙₜₑᵣ~6.471-6.7630.16em0ex. Magnetic measurements indicate no magnetic order down to 1.8 K for all family members. Specific heat characterizations on NaBa₃Nd₃Si₆O₂₀ and NaBa₃Gd₃Si₆O₂₀ reveal the formation of long-range magnetic order at TN~0.20 K and TN~0.42 K with large spin fluctuations at low temperatures. Furthermore, NaBa₃Gd₃Si₆O₂₀ exhibits a large magnetocaloric effect at temperatures below 1 K, making it an attractive candidate for sub-Kelvin magnetic refrigeration. The serial family compounds NaBa₃RE₃Si₆O₂₀ provide an ideal platform for exploring novel diamond spin chain physics involving $4f$ electrons.