B-Site Cu ^{2 +} Substitution and Strain-Mediated Magnetic Evolution in La ₂ CoRuO ₆ Double Perovskite: Insights from Experiment and DFT + U-Corrected Calculations

High Resolution Image Download MS PowerPoint Slide Understanding the magnetic ground states of double perovskites remains complex due to competing exchange interactions, spin–orbit coupling, and structural disorder. This study explores the substitution of Cu 2 + for Co 2 + in La 2 CoRuO 6 (LCRO), integrating experimental and DFT methods to probe the structural and electronic effects influencing magnetism. Pristine LCRO exhibits a monoclinic P 2 1 / c phase with dominant antiferromagnetic (AFM) Co 2 + –O–Ru 4 + interactions. Low-level Cu 2 + substitution ( x = 0.05 and 0.3) induces a strain-driven transformation to a tetragonal I 4/ m phase, introducing structural inhomogeneity and mixed valence states. These lead to competing ferromagnetic (FM) interactions (Cu 2 + –O–Ru 4 + /Cu 2 + ), while AFM order partially persists at x = 0.3 due to orbital asymmetry and strain effects. Magnetic measurements and DFT calculations show a Néel temperature ( T N ) shift from 28.7 to 39.8 K ( x = 0.05), and emerging FM behavior at 19.2 K. At x = 0.3, AFM suppression and a Curie temperature ( T C ) of 36.5 K reveal dominant FM pathways. Finite-size corrected Curie–Weiss analysis highlights the role of strain and particle size in modulating magnetic properties and restoring intrinsic behavior in larger particles.