Site dependent localized-delocalized magnetic moment in the magnetization-reversal in an inverse-spinel vanadate*

Neutron diffraction, magnetization, and muon spin relaxation measurements, complemented by density functional theory (DFT) calculations are employed to unravel the various magnetic phases of the inverse spinel Co₂VO₄.  All measurements show a second-order magnetic phase transition at T_C = 168 K to a  colinear ferrimagnetic phase. DFT and the experimental results indicate the moments in the ferrimagnetic phase are delocalized and undergo gradual localization as the temperature is lowered below T_C . The delocalized-localized crossover gives rise to a maximum magnetization at T_NC = 138 K with a continuous decrease in the magnetization and sign-change at  T_MR= 65 K. The magnetization reversal determined at zero fields is found to be highly sensitive to an applied magnetic field, such that above B= 0.03 T, instead of a reversal, a minimum in the magnetization is apparent at T_MR. Analysis of the neutron diffraction measurements shows that the magnetization reversal is due to a gradual change in the-nearly ferromagnetic A and B sub-lattices that grow differently as the temperatures are lowered below T_C.   Muon measurements are consistent with the picture that the moments gradually become more localized as the temperature is lowered and at that at zero applied magnetic fields give rise to magnetization reversal or a minimum (at applied magnetic fields)  at T_MR.