Spin-1/2 Triangular Lattice with Orbital Degeneracy in a Metallic Oxide Ag2NiO2

TL;DR

This study investigates Ag2NiO2, a metallic oxide with a layered structure featuring a spin-1/2 triangular lattice and orbital degeneracy, revealing orbital and magnetic orderings along with electron mass enhancement.

Contribution

It provides detailed experimental characterization of Ag2NiO2's structure, magnetic, and electronic properties, highlighting the interplay of orbital degeneracy and itinerant electrons in a novel metallic oxide.

Findings

Orbital ordering at 260 K

Antiferromagnetic ordering at 56 K

Significant electron mass enhancement

Abstract

A novel metallic and magnetic transition metal oxide Ag2NiO2 is studied by means of resistivity, magnetic susceptibility, specific heat and X-ray diffraction. The crystal structure is characterized by alternating stacking of a Ni3+O2 layer and a (Ag2)+ layer, the former realizing a spin-1/2 triangular lattice with eg orbital degeneracy and the latter providing itinerant electrons. It is found that the NiO2 layer exhibits orbital ordering at Ts = 260 K and antiferromagnetic spin ordering at TN = 56 K. Moreover, a moderately large mass enhancement is found for the itinerant electrons, suggesting a significant contribution from the nearly localized Ni 3d state to the Ag 5s state that forms a broad band.