Unravelling the local structure and magnetic dynamics of Cu-doped MnV₂O₄

The interplay between local structure, electronic structure, and magnetism was investigated in solid-state-synthesized Cu-incorporated MnV₂O₄. Powder X-ray diffraction (PXRD) measurements were caried out to investigate phase formation and structural evolution with Cu-doping for Cu-doped MnV2O4 samples. Systematic reduction in the lattice constant and interatomic bond lengths was observed with Cu doping due to the smaller ionic radii of Cu²⁺ compared to Mn²⁺. X-ray absorption spectroscopy reveals an increase in the oxidation state of V from ~3.42 to ~3.75 with Cu-doping, while the oxidation states of Mn and Cu remain stable at ~2.05 to ~2.20 and ~1.00, respectively. Increased V oxidation state results in a decrease in magnetic moments of V, so overall the weakening of A and B sites magnetic moments due to Cu doping, is responsible for the decrease in magnetic transition temperature of Cu-doped MnV₂O₄ samples. Due to Cu-doping local disorder at the Cu site was stronger, followed by the V site due to nearest neighbour interactions between the Cu-V path, while the Mn site was stable. Density functional calculation shows strong hybridization between V and O, causing charge and spin transfer, while Mn remains localized deep inside the valence band. V-V exchange coupling shows domination, followed by Mn-V exchange coupling, and Mn-Mn exchange coupling remains relatively weak. With Cu-doping, V-V and Mn-V exchange coupling weaken, while Mn-Mn exchange coupling shows slight improvement, indicating new interaction pathways due to Cu-doping.