Spin-phonon coupling in K${}_{0.8}$Fe${}_{1.6}$Se${}_{2}$ and KFe${}_{2}$Se${}_{2}$: Inelastic neutron scattering and ab initio phonon calculations

Spin-phonon coupling in K $_{0.8}$ Fe $_{1.6}$ Se $_{2}$ and KFe $_{2}$ Se $_{2}$ : Inelastic neutron scattering and ab initio phonon calculations

R. Mittal, M. K. Gupta, S. L. Chaplot, M. Zbiri, S. Rols, H. Schober, Y. Su, Th. Brueckel, and T. Wolf

Phys. Rev. B 87, 184502 – Published 3 May 2013

Abstract

We report measurements of the temperature dependence of phonon densities of states in K $_{0.8}$ Fe $_{1.6}$ Se $_{2}$ using inelastic neutron scattering technique. While cooling down to 150 K, a phonon peak splitting ∼25 meV is observed and a new peak appears at 31 meV. The measurements support the recent Raman and infrared measurements, indicating a lowering of symmetry of K $_{0.8}$ Fe $_{1.6}$ Se $_{2}$ upon cooling below 250 K. Ab initio phonon calculations have been carried out for K $_{0.8}$ Fe $_{1.6}$ Se $_{2}$ and KFe $_{2}$ Se $_{2}$ . The comparison of the phonon spectra as obtained from the magnetic and nonmagnetic calculations show pronounced differences. We show that in the two calculations, the energy range of the vibrational contribution from both Fe and Se are quite different. We conclude that Fe magnetism is correlated to the phonon dynamics and plays an important role in stabilizing the structure of K $_{0.8}$ Fe $_{1.6}$ Se $_{2}$ , as well as that of KFe $_{2}$ Se $_{2}$ . The calculations highlight the presence of low energy optical vibrational modes in K $_{0.8}$ Fe $_{1.6}$ Se $_{2}$ compared to KFe $_{2}$ Se $_{2}$ .

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Received 23 January 2013

DOI:https://doi.org/10.1103/PhysRevB.87.184502

Authors & Affiliations

R. Mittal¹, M. K. Gupta¹, S. L. Chaplot¹, M. Zbiri², S. Rols², H. Schober^2,3, Y. Su⁴, Th. Brueckel^4,5, and T. Wolf⁶

¹Solid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
²Institut Laue-Langevin, BP 156, 38042 Grenoble Cedex 9, France
³Université Joseph Fourier, UFR de Physique, 38041, Grenoble Cedex 9, France
⁴Juelich Centre for Neutron Science JCNS-FRM II, Forschungszentrum Juelich GmbH, Outstation at FRM II, Lichtenbergstr. 1, D-85747 Garching, Germany
⁵Juelich Centre for Neutron Science JCNS and Peter Gruenberg Institut PGI, JARA-FIT, Forschungszentrum Juelich GmbH, 52425 Juelich, Germany
⁶Institut fuer Festkoerperphysik, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany

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Issue

Vol. 87, Iss. 18 — 1 May 2013

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