Preferential Site Ordering Alters the Magnetic Behavior of Sm₃Ru₄Sn_{13–<i>x</i>}Ge_<i>x</i> (<i>x</i> = 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, Sm₃Ru₄Sn_13-<i>x</i>Ge_<i>x</i> (<i>x</i> = 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 <i>Pm</i>3̅<i>n</i>, 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 <i>T</i>_N = 7.3 K. However, Sm₃Ru₄Sn₁₂Ge and Sm₃Ru₄Sn₁₁Ge₂ showed notably lower-temperature antiferromagnetic phase transitions with substantial peak broadening at <i>T</i>_N = 5.5 and 4.1 K, respectively. This work demonstrates that preferential substitution of Ge in Sm₃Ru₄Sn_13-<i>x</i>Ge_<i>x</i> allows for more precise tunability of its magnetic structure, elucidating design principles for new quantum phases.