Spin-dependent orbital selectivity and partial Kondo-screening in magnetically ordered Hund's metal

Abstract

Hund's metallicity in 3$d$ transition metal oxides constitutes a rare class of compounds, since they have been long understood considering the dominance of Hubbard $U$. $\mathrm{LiV_2O_4}$\& $\mathrm{Sr_2CoO_4}$ belong to this rare class of metals; among them, $\mathrm{LiV_2O_4}$ has been the subject of extensive investigations for its unconventional heavy-fermion behavior, while studies on $\mathrm{Sr_2CoO_4}$ remain limited despite its anomalous ferromagnetic ground state. In this study, we report an unusual spin-orbital selective localization in $\mathrm{Sr_2CoO_4}$ leading to a sharp Kondo resonance at $\sim$70 K in the spin-$up$ channel of orbitals of $t_{2g}$ symmetry using a combination of Density functional theory and Dynamical mean field theory (DFT+DMFT) calculations. Correspondingly, an appreciable reduction in the magnetization below $T$=100 K further suggests partial Kondo screening of local moments active at low temperatures, explaining its effective spin magnetization state and upturn in its resistivity observed in experimental reports. We note a significant effect of Hund's induced spin-orbital selective incoherence in dictating the temperature evolution of its macroscopic observables e.g. spin-spin correlation function and effective local moment. Our results reveal a potentially distinct/new form of spin-dependent selectivity induced via Hund's coupling in addition to the conventional orbital-selectivity in the Hund's metals, as a plausible key mechanism in stabilizing their long-range magnetic order.