Determining the Anisotropic Exchange Coupling of CrO_2 via First-Principles Density Functional Theory Calculations

TL;DR

This study uses first-principles density functional theory to analyze anisotropic exchange interactions in CrO_2, calculating exchange energies, spin-wave stiffness, and Curie temperature, and evaluating the accuracy of DFT methods.

Contribution

It introduces a comprehensive DFT-based approach combining supercell and spin-spiral methods to determine exchange interactions and magnetic properties of CrO_2.

Findings

Calculated exchange energies and spin-wave stiffness constants.

Predicted Curie temperature consistent with experimental data.

Evaluated the accuracy of DFT methods for magnetic interactions.

Abstract

We report a study of the anisotropic exchange interactions in bulk CrO_2 calculated from first principles within density functional theory. We determine the exchange coupling energies, using both the experimental lattice parameters and those obtained within DFT, within a modified Heisenberg model Hamiltonian in two ways. We employ a supercell method in which certain spins within a cell are rotated and the energy dependence is calculated and a spin-spiral method that modifies the periodic boundary conditions of the problem to allow for an overall rotation of the spins between unit cells. Using the results from each of these methods, we calculate the spin-wave stiffness constant D from the exchange energies using the magnon dispersion relation. We employ a Monte Carlo method to determine the DFT-predicted Curie temperature from these calculated energies and compare with accepted values. Finally, we offer an evaluation of the accuracy of the DFT-based methods and suggest implications of the competing ferro- and antiferromagnetic interactions.