Tunable Magnetic Frustration in the Cu-Ru-based Double Perovskite La$_{2-x}$Sm$_x$CuRuO$_6$ (x = 0, 1, 2) Oxides
In this study, we investigate structural, magnetic, and electronic properties of the copper-ruthenate based oxide double perovskite La$_{2-x}$Sm$_x$CuRuO$_6$ (x = 0, 1, 2), synthesized through the solid-state reaction method. X-ray diffraction analysis reveals that all compounds crystallize in a monoclinic symmetry, with varying degree of structural distortion that increases in moving from La$^{3+}$ to smaller size cation Sm$^{3+}$. Electrical resistivity studies indicate insulating behaviour in all compounds, with variable-range-hopping domination at low temperatures, due to presence of anti-site disorder. AC susceptibility and heat capacity measurements suggest suppression of frustration in Sm-bearing compounds, affecting the magnetic behavior. Our first-principles calculations suggest that the combined effects of lattice distortion and Sm magnetism play a crucial role in weakening magnetic frustration, thereby rationalizing the experimental observations. These findings shed light on the complex interplay of crystal structure and magnetism in Cu-Ru double perovskites, and open up an avenue for tuning of magnetic properties through rare-earth-ion substitution.