Magnetic interactions in strongly correlated systems: spin and orbital contributions

TL;DR

This paper introduces a comprehensive method to derive detailed magnetic interaction parameters, including relativistic effects and orbital contributions, from electronic models, enabling precise modeling of complex magnetic systems.

Contribution

It provides a unified, exact framework to extract complete relativistic exchange tensors and separate spin, orbital, and spin-orbital magnetic contributions from electronic Green's functions.

Findings

Derived complete relativistic exchange tensors including Dzyaloshinskii-Moriya interactions.

Unified framework accounts for non-local self-energies and two-particle Green's function vertices.

Method distinguishes spin, orbital, and spin-orbital magnetic contributions.

Abstract

We present a technique to map an electronic model with local interactions (a generalized multi-orbital Hubbard model) onto an effective model of interacting classical spins, by requiring that the thermodynamic potentials associated to spin rotations in the two systems are equivalent up to second order in the rotation angles. This allows to determine the parameters of relativistic and non-relativistic magnetic interactions in the effective spin model in terms of equilibrium Green's functions of the electronic model. The Hamiltonian of the electronic system includes, in addition to the non-relativistic part, relativistic single-particle terms such as the Zeeman coupling to an external magnetic fields, spin-orbit coupling, and arbitrary magnetic anisotropies; the orbital degrees of freedom of the electrons are explicitly taken into account. We determine the complete relativistic exchange tensors, accounting for anisotropic exchange, Dzyaloshinskii-Moriya interactions, as well as additional non-diagonal symmetric terms (which may include dipole-dipole interaction). Our procedure provides the complete exchange tensors in a unified framework, including previously disregarded features such as the vertices of two-particle Green's functions and non-local self-energies. We do not assume any smallness in spin-orbit coupling, so our treatment is in this sense exact. Finally, we show how to distinguish and address separately the spin, orbital and spin-orbital contributions to magnetism.