This title appears in the Scientific Report : 2014 

Spin Excitations in Solids from Many-Body Perturbation Theory
Friedrich, Christoph (Corresponding Author)
Şaşıoğlu, Ersoy / Müller, Mathias Christian Thomas David / Schindlmayr, Arno / Blügel, Stefan
Quanten-Theorie der Materialien; IAS-1
Quanten-Theorie der Materialien; PGI-1
2014
First Principles Approaches to Spectroscopic Properties of Complex Materials
Berlin, Heidelberg Springer Berlin Heidelberg 2014
259 - 301
978-3-642-55068-3 (electronic)
978-3-642-55067-6 (print)
10.1007/128_2013_518
Contribution to a book
Spin-based and quantum information
Topics in Current Chemistry 347
Please use the identifier: http://dx.doi.org/10.1007/128_2013_518 in citations.
Collective spin excitations form a fundamental class of excitations in magnetic materials. As their energy reaches down to only a few meV, they are present at all temperatures and substantially influence the properties of magnetic systems. To study the spin excitations in solids from first principles, we have developed a computational scheme based on many-body perturbation theory within the full-potential linearized augmented plane-wave (FLAPW) method. The main quantity of interest is the dynamical transverse spin susceptibility or magnetic response function, from which magnetic excitations, including single-particle spin-flip Stoner excitations and collective spin-wave modes as well as their lifetimes, can be obtained. In order to describe spin waves we include appropriate vertex corrections in the form of a multiple-scattering T matrix, which describes the coupling of electrons and holes with different spins. The electron–hole interaction incorporates the screening of the many-body system within the random-phase approximation. To reduce the numerical cost in evaluating the four-point T matrix, we exploit a transformation to maximally localized Wannier functions that takes advantage of the short spatial range of electronic correlation in the partially filled d or f orbitals of magnetic materials. The theory and the implementation are discussed in detail. In particular, we show how the magnetic response function can be evaluated for arbitrary k points. This enables the calculation of smooth dispersion curves, allowing one to study fine details in the k dependence of the spin-wave spectra. We also demonstrate how spatial and time-reversal symmetry can be exploited to accelerate substantially the computation of the four-point quantities. As an illustration, we present spin-wave spectra and dispersions for the elementary ferromagnet bcc Fe, B2-type tetragonal FeCo, and CrO2 calculated with our scheme. The results are in good agreement with available experimental data.