Planar spin exchange in LiNiO_2

TL;DR

This paper investigates the microscopic origins of spin exchange interactions in LiNiO2, revealing how trigonal crystal field effects lead to mixed ferromagnetic and antiferromagnetic couplings, explaining experimental observations.

Contribution

It provides a theoretical framework showing how trigonal crystal fields induce antiferromagnetic exchange in LiNiO2, challenging traditional rules.

Findings

Trigonal crystal field splitting causes antiferromagnetic exchange.

Coexistence of ferromagnetic and antiferromagnetic couplings explained.

Microscopic foundation for experimental magnetic behavior established.

Abstract

We study the planar spin exchange couplings in LiNiO2 using a perturbative approach. We show that the inclusion of the trigonal crystal field splitting at the Oxygen sites leads to the appearance of antiferromagnetic exchange integrals in deviation from the Goodenough-Kanamori-Anderson rules for this 90 degree bond. That gives a microscopic foundation for the recently observed coexistence of ferromagnetic and antiferromagnetic couplings in the orbitally-frustrated state of LiNiO2. (F. Reynaud et al, Phys. Rev. Lett. 86, 3638 (2001))