Altermagnetism and Anomalous Transport in Ag$^{2+}$ Fluorides: KAgF$_3$ and K$_2$AgF$_4$

TL;DR

This paper investigates the magnetic and transport properties of Ag$^{2+}$ fluoride compounds, revealing altermagnetic behavior and anomalous transport phenomena in KAgF$_3$, while contrasting it with the conventional antiferromagnetic K$_2$AgF$_4$.

Contribution

It demonstrates the presence of altermagnetism and associated anomalous transport effects in KAgF$_3$, a novel finding in Ag-based fluoride compounds, supported by first-principles calculations.

Findings

KAgF$_3$ exhibits collinear A-type antiferromagnetic order with orbital ordering.

KAgF$_3$ shows anomalous Hall, Nernst, and thermal Hall effects.

K$_2$AgF$_4$ behaves as a conventional antiferromagnet with no anomalous Hall response.

Abstract

Compounds containing Ag$^{2+}$ ion with 4d$^9$ configuration will cause significant Jahn-Teller distortions and orbital ordering. Such orbital order is closely related to the magnetic coupling, according to Goodenough-Kanamori Ruels. Our first-principles calculations reveal that the ground state of KAgF$_3$ exhibits collinear A-type antiferromagnetic (A-AFM) ordering accompanied by C-type orbital ordering. In contrast, K$_2$AgF$_4$ adopts a collinear intralayer antiferromagnetic configuration coupled with ferromagnetic orbital ordering. The A-AFM KAgF$_3$ presents distinct altermagnetic responses, including: (i) prominent anomalous transport effects, such as anomalous Hall conductivity (AHC), anomalous Nernst conductivity (ANC), and thermal anomalous Hall conductivity (TAHC); and (ii) strong magneto-optical responses, manifested through pronounced Kerr and Faraday effects. On the other hand, K$_2$AgF$_4$ behaves as a conventional collinear antiferromagnet preserving $\mathcal{PT}$ symmetry, hence precluding the emergence of an anomalous Hall response.