From localized 4f electrons to anisotropic exchange interactions in ferromagnetic CeRh6Ge4

TL;DR

This study investigates the magnetic interactions in CeRh6Ge4, revealing isotropic and anisotropic exchange interactions that influence its ferromagnetic and quantum critical properties.

Contribution

The paper combines density functional theory and dynamical mean-field theory to analyze the anisotropic exchange interactions in CeRh6Ge4, highlighting the role of 4f electrons.

Findings

Nearest-neighbor ferromagnetic interaction is isotropic along c axis.

Inter-chain coupling is highly anisotropic, with in-plane ferromagnetic and out-of-plane antiferromagnetic components.

Magnetic anisotropy and 4f wavefunctions underpin the ferromagnetic transition and quantum criticality.

Abstract

CeRh6Ge4 is a cerium-based ferromagnetic material exhibiting a quantum critical behavior under pressure. We derive effective exchange interactions, using the framework of density functional theory combined with dynamical mean-field theory. Our results reveal that the nearest-neighbor ferromagnetic interaction along the c axis is isotropic in spin space, leading to a formation of spin chains. On the other hand, the inter-chain coupling is highly anisotropic: The in-plane moment weakly interacts ferromagnetically in the a--b plane to stabilize the ferromagnetic state, whereas the z-component couples antiferromagnetically, contributing to its destabilization. The magnetic anisotropy of the interchain interactions as well as of the local 4f wavefunctions characterizes the magnetic properties underlying the ferromagnetic transition and the quantum critical behavior in CeRh6Ge4.