Journal Article

PreJuSER-18474

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Terahertz and infrared spectroscopic evidence of phonon-paramagnon coupling in hexagonal piezomagnetic YMnO3

Kadlec, C. ; Goian, V. ; Rushchanskii, K. Z.FZJ* ; Kuzel, P. ; Lezaic, M.FZJ* ; Kohn, K. ; Pisarev, R. V. ; Kamba, S.

2011
APS College Park, Md.

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Please use a persistent id in citations: http://hdl.handle.net/2128/10897  doi:10.1103/PhysRevB.84.174120

Abstract: Terahertz and far-infrared electric and magnetic responses of hexagonal piezomagnetic YMnO3 single crystals are investigated. Antiferromagnetic resonance is observed in the spectra of magnetic permeability mu(a) [H(omega) oriented within the hexagonal plane] below the Neel temperature T-N. This excitation softens from 41 to 32 cm(-1) upon heating and finally disappears above T-N. An additional weak and heavily-damped excitation is seen in the spectra of complex dielectric permittivity epsilon(c) within the same frequency range. This excitation contributes to the dielectric spectra in both antiferromagnetic and paramagnetic phases. Its oscillator strength significantly increases upon heating toward room temperature, thus providing evidence of piezomagnetic or higher-order couplings to polar phonons. Other heavily-damped dielectric excitations are detected near 100 cm(-1) in the paramagnetic phase in both epsilon(c) and epsilon(a) spectra, and they exhibit similar temperature behavior. These excitations appearing in the frequency range of magnon branches well below polar phonons could remind electromagnons, however their temperature dependence is quite different. We have used density functional theory for calculating phonon dispersion branches in the whole Brillouin zone. A detailed analysis of these results and of previously published magnon dispersion branches brought us to the conclusion that the observed absorption bands stem from phonon-phonon and phonon-paramagnon differential absorption processes. The latter is enabled by strong short-range in-plane spin correlations in the paramagnetic phase.

Keyword(s): J

Note: The authors thank M. Mostovoy for valuable discussions. This work was supported by the Czech Science Foundation (Project No. 202/09/0682), by AVOZ10100520, and by the Young Investigators Group Program of the Helmholtz Association (Contract VH-NG-409). The contribution of Ph.D. student V.G. has been supported by Project Nos. 202/09/H041 and SVV-2011-263303. R.V.P. acknowledges the support by the RFBR (Project No. 09-02-00070). The support of the Julich Supercomputing Center is gratefully acknowledged.

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Contributing Institute(s):

1. Quanten-Theorie der Materialien (PGI-1)
2. Quanten-Theorie der Materialien (IAS-1)

Research Program(s):

1. Grundlagen für zukünftige Informationstechnologien (P42)

Appears in the scientific report 2011

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