Origin of ferromagnetism in Cs$_2$AgF$_4$: importance of Ag - F covalency

TL;DR

This study uses density functional calculations to reveal that the ferromagnetism in Cs$_2$AgF$_4$ originates from strong Ag-F covalency and itinerant electron behavior, with significant F moments and a Stoner instability.

Contribution

It demonstrates the importance of Ag-F covalency and itinerant electron mechanisms in the ferromagnetism of Cs$_2$AgF$_4$, providing new insights into its magnetic origin.

Findings

Ground state is ferromagnetic and nearly half metallic.

Strong hybridization of Ag-$d$ and F-$p$ states observed.

Substantial magnetic moments on F atoms due to covalency.

Abstract

The magnetic nature of Cs$_{2}$AgF$_{4}$, an isoelectronic and isostructural analogue of La$_2$CuO$_4$, is analyzed using density functional calculations. The ground state is found to be ferromagnetic and nearly half metallic. We find strong hybridization of Ag-$d$ and F-$p$ states. Substantial moments reside on the F atoms, which is unusual for the halides and reflects the chemistry of the Ag(II) ions in this compound. This provides the mechanism for ferromagnetism, which we find to be itinerant in character, a result of a Stoner instability enhanced by Hund's coupling on the F.