Orbitally induced hierarchy of exchange interactions in zigzag antiferromagnetic state of honeycomb silver delafossite Ag3Co2SbO6

TL;DR

This study investigates the magnetic structure and interactions in honeycomb silver delafossite Ag3Co2SbO6, revealing a hierarchy of exchange interactions influenced by orbital degrees of freedom, and identifies a field-induced spin-flop transition.

Contribution

The paper provides a detailed analysis of the magnetic interactions and structure of Ag3Co2SbO6, highlighting the orbital-driven hierarchy of exchange interactions and the magnetic phase diagram, which were not previously characterized.

Findings

Antiferromagnetic order at TN ~ 21.2 K.

Field-induced spin-flop transition below TN.

Hierarchy of exchange interactions influenced by orbital degrees of freedom.

Abstract

We report the revised crystal structure, static and dynamic magnetic properties of quasi-two dimensional honeycomb-lattice silver delafossite Ag3Co2SbO6. The magnetic susceptibility and specific heat data are consistent with the onset of antiferromagnetic long range order at low temperatures with N\'eel temperature TN ~ 21.2 K. In addition, the magnetization curves revealed a field-induced (spin-flop type) transition below TN in moderate magnetic fields. The GGA+U calculations show the importance of the orbital degrees of freedom, which maintain a hierarchy of exchange interaction in the system. The strongest antiferromagnetic exchange coupling was found in the shortest Co-Co pairs and is due to direct and superexchange interactions between the half-filled xz+yz orbitals pointing directly to each other. The other four out of six nearest neighbor exchanges within the cobalt hexagon are suppressed, since for these bonds active half-filled orbitals turned out to be parallel and do not overlap. The electron spin resonance (ESR) spectra reveal a Gaussian shape line attributed to Co2+ ion in octahedral coordination with average effective g-factor g=2.3+/-0.1 at room temperature and shows strong divergence of ESR parameters below 120 K, which imply an extended region of short-range correlations. Based on the results of magnetic and thermodynamic studies in applied fields, we propose the magnetic phase diagram for the new honeycomb-lattice delafossite.