Electronic structure and magnetism of a ferromagnetic insulator Cs2AgF4: explanation for a lilac colour and a prediction for the anisotropic g factor

TL;DR

This paper models the electronic structure and magnetic properties of Cs2AgF4, explaining its lilac color and predicting an anisotropic g factor, with results consistent with experimental observations and providing testable predictions.

Contribution

It offers a detailed theoretical explanation for Cs2AgF4's insulating and magnetic properties, including color and g factor predictions, considering strong correlations and spin-orbit coupling.

Findings

Insulating ground state with a 2.6 meV spin gap

Lilac color explained by d-d excitation at 2.0-2.3 eV

Predicted anisotropic g factors (gz=2.12, gy=2.52)

Abstract

Magnetic properties of stechiometric Cs2AgF4 have been calculated within a very strong correlation limit taking into account a low-symmetry crystal field and the intra-atomic spin-orbit coupling of the Ag2+ ion. We consistently explain the insulating ground state and the magnetic state revealing the spin gap of 2.6 meV below Tc of 14.9 K. A d-d excitation of 2.0-2.3 eV related to the t2g-eg promotion energy (=10Dq) is a reason for the lilac colour of Cs2AgF4. Our approach can be experimentally verified by the measurement of the g factor (gz =2.12 and gy =2.52) and the absorption energy at 2.0-2.3 eV.