Orbital order and partial electronic delocalization in a triangular magnetic metalAg2MnO2

Abstract

Magnetic and electrical properties of ${\text{Ag}}_{2}{\text{MnO}}_{2}$ were examined by elastic and inelastic neutron-scattering measurements and by density-functional calculations. The spins of the triangular antiferromagnet metal ${\text{Ag}}_{2}{\text{MnO}}_{2}$ are found to freeze into a gapless short-range collinear state below 50 K because of a ferro-orbital ordering and spin-orbit coupling of the high-spin ${\text{Mn}}^{3+}$ ions. The decrease in the spin-spin correlation lengths of ${\text{Ag}}_{2}{\text{MnO}}_{2}$ in the order, ${\ensuremath{\xi}}_{b}⪢{\ensuremath{\xi}}_{a}⪢{\ensuremath{\xi}}_{c}$, is explained by the spin-exchange interactions calculated for the ferro-orbital ordered state. The electronic states around the Fermi level have significant contributions from the spin-polarized $\text{Mn}\text{ }3d$ and $\text{O}\text{ }2p$ states, which makes electron-electron scattering dominate over electron-phonon scattering at low temperatures leading to the $\ensuremath{\rho}\ensuremath{\propto}{T}^{2}$ behavior below 50 K.