Tunable Frustrated Magnetism and Charge Transport in La-Substituted Y ₂ Ru ₂ O ₇ Pyrochlore Ruthenates

We report a comprehensive study of the structural, magnetic, and electrical properties of La-substituted Y2Ru2O7 pyrochlore ruthenates. While the synthesis of pure La2Ru2O7 remains elusive, partial substitution of La3+ into Y2Ru2O7 is achievable, providing a tunable platform to systematically modify the lattice. The larger ionic radius of La3+ expands the lattice, potentially altering the Ru 4d bandwidth and magnetic exchange pathways. The compound Y1.75La0.25Ru2O7 thus bridges the gap between well-characterized Y2Ru2O7 and hypothetical La2Ru2O7, enabling a controlled investigation of A-site size effects, local structural distortions, and their impact on frustrated magnetism and correlated electronic behavior. As a nonmagnetic dopant, La3+ isolates lattice effects on the Ru sublattice without introducing additional magnetic contributions. Magnetic measurements reveal a systematic suppression of antiferromagnetic ordering and a reduction of magnetic frustration, along with field-insensitive spin-glass-like behavior, consistent with geometrically frustrated magnetism. Electrical transport measurements indicate semiconducting behavior over the entire temperature range. The temperature-dependent resistivity follows Mott’s three-dimensional variable-range hopping model, and the onset of Ru 4d spin ordering significantly modifies carrier scattering, leading to pronounced resistivity anomalies near the magnetic transition.