On the Ferrimagnetic State of CrCl$_2$(pyz)$_2$

TL;DR

This paper presents a minimal Hubbard model to understand the ferrimagnetic state of CrCl₂(pyz)₂, predicting magnetic moments and interactions consistent with experimental data, aiding the design of magnetic metal-organic frameworks.

Contribution

It introduces a theoretical Hubbard model capturing the ferrimagnetic properties of CrCl₂(pyz)₂, aligning with experimental magnetic moments and interactions.

Findings

Predicted magnetic moment of 2μ_B close to experimental 1.8μ_B.

Estimated weak ferromagnetic Cr-Cr coupling of ~0.9 meV.

RKKY interaction suggests Cr-Cr coupling of ~5 meV.

Abstract

Van der Waals layered ferromagnetic compounds with high two-dimensional electronic conductivity holds strong potential for quantum computing, future unconventional superconductors, catalysts, batteries, and fuel cells. We suggest a minimal theoretical model to understand the magnetic properties of the metal-organic framework CrCl$_2$(pyz)$_2$ (pyz=pyrazine). Using a Hubbard model we show that the groundstate is dominated by a specific configuration of delocalized electrons on the pyz sites with a ferrimagnetic coupling to the localized spins on the Cr sites. This model suggests a magnetic moment of $2\mu_B$ which is remarkably close to the experimental value of $1.8 \mu_B$ [K. S. Pedersen et al., Nat. Chem. 10, 1056-1061 (2018)]. From Weiss mean-field theory we predict a weak ferromagnetic Cr-Cr coupling of $\approx 0.9$ meV. This is consolidated by second order perturbation theory of the RKKY interaction yielding a Cr-Cr coupling of $\approx 5$ meV. Understanding the interactions in these types of compounds can facilitate designs of metal-organic compounds with tailored magnetic properties.