Anharmonic effect on lattice distortion, orbital ordering and magnetic properties in Cs2AgF4

TL;DR

This paper introduces a cluster self-consistent field method to study how anharmonic lattice distortions influence orbital ordering and ferromagnetism in Cs2AgF4, aligning theoretical results with experimental data.

Contribution

It develops a novel approach incorporating anharmonic effects to explain the stabilization of ferromagnetism in Cs2AgF4.

Findings

Anharmonic distortions stabilize ferromagnetic ground state.

Lattice distortion amplitudes match experimental values.

Magnetic coupling and moments agree with observations.

Abstract

We develop the cluster self-consistent field method incorporating both electronic and lattice degrees of freedom to study the origin of ferromagnetism in Cs$_{2}$AgF$_{4}$. After self-consistently determining the harmonic and anharmonic Jahn-Teller distortions, we show that the anharmonic distortion stabilizes the staggered x$^{2}$-z$^{2}$/y$^{2}$-z$^{2}$ orbital and ferromagnetic ground state, rather than the antiferromagnetic one. The amplitudes of lattice distortions, Q$_{2}$ and Q$_{3}$, the magnetic coupling strengthes, J$_{x,y}$, and the magnetic moment, are in good agreement with the experimental observation.