First-Principles Study of Exchange Interactions of Yttrium Iron Garnet

TL;DR

This study uses first-principles calculations to accurately determine exchange interactions in Yttrium Iron Garnet, aligning theoretical models with experimental data and highlighting the method's limitations.

Contribution

It provides a first-principles approach to calculate exchange constants in Yttrium Iron Garnet, improving consistency with experimental observations.

Findings

Calculated exchange constants match experimental Curie temperature

Magnon spectrum agrees with neutron scattering data

Identified limitations in optical mode frequency predictions

Abstract

Yttrium Iron Garnet is the ubiquitous magnetic insulator used for studying pure spin currents. The exchange constants reported in the literature vary considerably between different experiments and fitting procedures. Here we calculate them from first-principles. The local Coulomb correction (U - J) of density functional theory is chosen such that the parameterized spin model reproduces the experimental Curie temperature and a large electronic band gap, ensuring an insulating phase. The magnon spectrum calculated with our parameters agrees reasonably well with that measured by neutron scattering. A residual disagreement about the frequencies of optical modes indicates the limits of the present methodology.