Preferential Site Ordering Alters the Magnetic Behavior of Sm₃Ru₄Sn13–xGex (x = 0–2)

An important aspect of materials research is the ability to tune different physical properties through controlled crystallographic site substitution. The Remeika phase Ln3M4X13 (Ln = Lanthanide, M = Transition Metal, X = Tetrel), often referred to as a "filled skutterudite," is of interest due to the tunability of its constituent components and their effects on physical properties, such as superconductivity and complex magnetism. In this work, Sm3Ru4Sn13–xGex (x = 0–2) was synthesized via excess Sn-flux and characterized using powder and single-crystal X-ray diffraction, magnetometry, X-ray photoelectron spectroscopy, and heat capacity. Sm3Ru4Sn13 and its Ge-solid-solution members crystallize in cubic symmetry with the space group Pm3̅n, which has two unique Wyckoff positions for the tetrel (X) site. In the solid solution members, Ge shows a preferential occupancy for one of the two Wyckoff sites. Magnetometry and heat capacity measurements of Sm3Ru4Sn13 indicated antiferromagnetic ordering at TN = 7.3 K. However, Sm3Ru4Sn12Ge and Sm3Ru4Sn11Ge2 showed notably lower-temperature antiferromagnetic phase transitions with substantial peak broadening at TN = 5.5 and 4.1 K, respectively. This work demonstrates that preferential substitution of Ge in Sm3Ru4Sn13–xGex allows for more precise tunability of its magnetic structure, elucidating design principles for new quantum phases.