Localized-delocalized crossover of spin-carriers and magnetization reversal in Co$_{2}$VO$_{4}$

Abstract

Neutron diffraction, magnetization and muon spin relaxation measurements, supplemented by density functional theory (DFT) calculations are employed to unravel temperature-driven magnetization reversal (MR) in inverse spinel Co2VO4. All measurements show a second order magnetic phase transition at TC = 168 K to a collinear ferrimagnetic phase. The DFT results suggest the moments in the ferrimagnetic phase are delocalized and undergo gradual localization as the temperature is lowered below TC. The delocalized-localized crossover gives rise to a maximum magnetization at TNC = 138 K and the continuous decrease in magnetization produces sign-change at TMR ∼ 65 K. Muon spectroscopy results support the DFT, as a strong T1-relaxation is observed around TNC, indicating highly delocalized spin-carriers gradually tend to localization upon cooling. The magnetization reversal determined at zero field is found to be highly sensitive to applied magnetic field, such that above B ∼ 0.25 T instead of a reversal a broad minimum in the magnetization is apparent at TMR. Analysis of the neutron diffraction measurements shows two antiparallel magnetic sublattice-structure, each belonging to magnetic ions on two distinct crystal lattice sites. The relative balance of these two structural components in essence determines the magnetization. Indeed, the order parameter of the magnetic phase on one site develops moderately more than that on the other site. Unusual tipping of the magnetic balance, caused by such site-specific magnetic fluctuation, gives rise to a spontaneous flipping of the magnetization as the temperature is lowered. * A.B.K and C.B contributed equally.[1] M. Néel, Propriétés magnétiques des ferrites ; ferrimagnétisme et antiferromagnétisme, Annales De Physique 12, 137 (1948). [2] Y. Yafet and C. Kittel, Antiferromagnetic arrangements in ferrites, Physical Review 87, 290 (1952).