Magnetic susceptibility, exchange interactions and spin-wave spectra in the local spin density approximation

TL;DR

This paper revisits the calculation of exchange interactions and spin-wave spectra in itinerant ferromagnets using density functional theory, clarifying the optimal methods for different magnetic properties through ab initio calculations.

Contribution

It demonstrates that the original magnetic force theorem is best for magnon spectra, while the renormalized version suits static response functions, supported by calculations for Fe and Ni.

Findings

Original magnetic force theorem is optimal for magnon spectra.

Renormalized magnetic force theorem better describes static response.

Ab initio calculations confirm the theoretical conclusions.

Abstract

Starting from exact expression for the dynamical spin susceptibility in the time-dependent density functional theory a controversial issue about exchange interaction parameters and spin-wave excitation spectra of itinerant electron ferromagnets is reconsidered. It is shown that the original expressions for exchange integrals based on the magnetic force theorem (J. Phys. F14 L125 (1984)) are optimal for the calculations of the magnon spectrum whereas static response function is better described by the ``renormalized'' magnetic force theorem by P. Bruno (Phys. Rev. Lett. 90, 087205 (2003)). This conclusion is confirmed by the {\it ab initio} calculations for Fe and Ni.