Journal Article

PreJuSER-8915

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Wannier-function approach to spin excitations in solids

Sasioglu, E.FZJ* ; Schindlmayr, A. ; Friedrich, C.FZJ* ; Freimuth, F.FZJ* ; Blügel, S.FZJ*

2010
APS College Park, Md.

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Please use a persistent id in citations: http://hdl.handle.net/2128/10999  doi:10.1103/PhysRevB.81.054434

Abstract: We present a computational scheme to study spin excitations in magnetic materials from first principles. The central quantity is the transverse spin susceptibility, from which the complete excitation spectrum, including single-particle spin-flip Stoner excitations and collective spin-wave modes, can be obtained. The susceptibility is derived from many-body perturbation theory and includes dynamic correlation through a summation over ladder diagrams that describe the coupling of electrons and holes with opposite spins. In contrast to earlier studies, we do not use a model potential with adjustable parameters for the electron-hole interaction but employ the random-phase approximation. To reduce the numerical cost for the calculation of the four-point scattering matrix we perform a projection onto maximally localized Wannier functions, which allows us to truncate the matrix efficiently by exploiting the short spatial range of electronic correlation in the partially filled d or f orbitals. Our implementation is based on the full-potential linearized augmented-plane-wave method. Starting from a ground-state calculation within the local-spin-density approximation (LSDA), we first analyze the matrix elements of the screened Coulomb potential in the Wannier basis for the 3d transition-metal series. In particular, we discuss the differences between a constrained nonmagnetic and a proper spin-polarized treatment for the ferromagnets Fe, Co, and Ni. The spectrum of single-particle and collective spin excitations in fcc Ni is then studied in detail. The calculated spin-wave dispersion is in good overall agreement with experimental data and contains both an acoustic and an optical branch for intermediate wave vectors along the [1 0 0] direction. In addition, we find evidence for a similar double-peak structure in the spectral function along the [1 1 1] direction. To investigate the influence of static correlation we finally consider LSDA+U as an alternative starting point and show that, together with an improved description of the Fermi surface, it yields a more accurate quantitative value for the spin-wave stiffness constant, which is overestimated in the LSDA.

Keyword(s): J

Note: Fruitful discussions with Y. Mokrousov, G. Bihlmayer, M. Niesert, A. Gierlich, T. Miyake, and F. Aryasetiawan are gratefully acknowledged. This work was funded in part by the EU through the Nanoquanta Network of Excellence (Grant No. NMP4-CT-2004-500198), the European Theoretical Spectroscopy Facility e-I3 (Grant No. INFRA-2007-211956), and by the Deutsche Forschungsgemeinschaft through the Priority Programme 1145.

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Contributing Institute(s):

1. Quanten-Theorie der Materialien (IFF-1)
2. Quanten-Theorie der Materialien (IAS-1)
3. Jülich-Aachen Research Alliance - Fundamentals of Future Information Technology (JARA-FIT)
4. Jülich Aachen Research Alliance - High-Performance Computing (JARA-HPC)

Research Program(s):

1. Grundlagen für zukünftige Informationstechnologien (P42)
2. ETSF - European Theoretical Spectroscopy Facility I3 (211956) (211956)

Appears in the scientific report 2010

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