Coupling between magnon and ligand-field excitations in magnetoelectric ${\text{Tb}}_{3}{\text{Fe}}_{5}{\text{O}}_{12}$ garnet

Coupling between magnon and ligand-field excitations in magnetoelectric ${Tb}_{3} {Fe}_{5} O_{12}$ garnet

T. D. Kang, E. Standard, K. H. Ahn, A. A. Sirenko, G. L. Carr, S. Park, Y. J. Choi, M. Ramazanoglu, V. Kiryukhin, and S.-W. Cheong

Phys. Rev. B 82, 014414 – Published 15 July 2010

Abstract

The spectra of far-infrared transmission in ${Tb}_{3} {Fe}_{5} O_{12}$ magnetoelectric single crystals have been studied in the range between 15 and $100 {cm}^{- 1}$ , in magnetic fields up to 10 T, and for temperatures between 5 and 150 K. We attribute some of the observed infrared-active excitations to electric dipole transitions between ligand-field split states of ${Tb}^{3 +}$ ions. Anticrossing between the magnetic exchange excitation and the ligand-field transition occurs at the temperature between 60 and 80 K. The corresponding coupling energy for this interaction is $6 {cm}^{- 1}$ . Temperature-induced softening of the hybrid IR excitation correlates with the increase in the static dielectric constant. We discuss the possibility for hybrid excitations of magnons and ligand-field states and their possible connection to the magnetoelectric effect in ${Tb}_{3} {Fe}_{5} O_{12}$ .

Received 15 May 2010

DOI:https://doi.org/10.1103/PhysRevB.82.014414

Authors & Affiliations

T. D. Kang, E. Standard, K. H. Ahn, and A. A. Sirenko^*

Department of Physics, New Jersey Institute of Technology, Newark, New Jersey 07102, USA

G. L. Carr

National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973, USA

S. Park, Y. J. Choi, M. Ramazanoglu, V. Kiryukhin, and S.-W. Cheong

Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA

^*sirenko@njit.edu

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Vol. 82, Iss. 1 — 1 July 2010

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Figure 1
(Color online) Normalized far-IR transmission spectra for ${Tb}_{3} {Fe}_{5} O_{12}$ single crystal measured in a zero external magnetic field at $T = 5$ , 17, and 80 K: (a)–(c), respectively. The light propagation is along the [1 1 1] direction. Arrows indicate the frequencies of IR-active absorption lines. The weak intensity oscillations between 20 and $35 {cm}^{- 1}$ are the interference thickness fringes.Reuse & Permissions
Figure 2
(Color online) (a) Maps of the normalized transmitted intensity vs temperature and frequency for ${Tb}_{3} {Fe}_{5} O_{12}$ . The blue (dark) color corresponds to stronger absorption and red (light) color indicates high transmission. The transmission intensity scale is between 0 and 0.1. (b) Experimental values for the LF and the hybrid LF-M excitations. The results of the fit using Eq. (2) with the coupling constant $Δ_{LF-M} = 6 {cm}^{- 1}$ are shown with blue dashed curves. (c) $| LF ⟩$ and $| M ⟩$ wave-function amplitudes for the upper energy $| Ω_{LF-M}^{(2)} ⟩$ hybrid state.Reuse & Permissions
Figure 3
(Color online) (a) Temperature dependence for the oscillator strength for the two hybrid modes with the frequencies $Ω_{LF-M}^{(1)}$ and $Ω_{LF-M}^{(2)}$ . In the temperature range between 60 and 80 K the modes are strongly coupled and only their sum can be determined. (b) Total contribution of the hybrid modes to the static values of $ε (0, T)$ and $μ (0, T)$ calculated from the transmission spectra using Eq. (4). (c) The temperature-induced variation in the static dielectric constant for ${Tb}_{3} {Fe}_{5} O_{12}$ at zero magnetic field and at the magnetic field of 0.2 T (from Ref. 4).Reuse & Permissions
Figure 4
(Color online) (a) Maps of the normalized transmitted intensity vs magnetic field and frequency for ${Tb}_{3} {Fe}_{5} O_{12}$ at $T = 15 K$ and $H ∥ [1 1 1]$ . The blue (dark) color corresponds to stronger absorption while red (light) color indicates high transmission. The transmission intensity scale is between 0 and 0.2. (b) Variation in the LF, magnon, and phonon excitations in magnetic field $H ∥ [1 1 1]$ . The linear slopes for magnetic field dependence for $Ω_{LF-M}^{(1)}$ , $Ω_{LF-M}^{(2)}$ , and $Ω_{LF-M}^{(3)}$ excitations are $1 μ_{B}$ , $- 1.5 μ_{B}$ , and $7 μ_{B}$ , respectively.Reuse & Permissions
Figure 5
(Color online) (a) Normalized far-IR transmission spectra for ${Tb}_{3} {Fe}_{5} O_{12}$ single crystal measured at $T = 5 K$ for external magnetic field $H = 0$ , 0.3, 0.6, and 0.9 T. Both, the light propagation and magnetic field are along the [1 0 0] direction. Arrows indicate the frequencies of two hybrid modes: $Ω_{LF-M}^{(2)}$ and $Ω_{LF-M}^{(3)}$ . (b) Variation in the coupled LF-M excitations $Ω_{LF-M}^{(2)}$ and $Ω_{LF-M}^{(3)}$ in magnetic field $H ∥ [1 0 0]$ . Blue solid lines are fits using Eq. (5) for coupled excitations. Dashed lines are strong-field approximations for uncoupled excitations.Reuse & Permissions
Figure 6
(Color online) (a) Maps of the normalized transmitted intensity vs magnetic field $H ∥ [1 1 1]$ measured at $T = 40 K$ . The transmission intensity scale is between 0 and 0.07. (b) Results of the fit for the oscillator strengths for two low-frequency hybrid modes: $Ω_{LF-M}^{(1)}$ and $Ω_{LF-M}^{(2)}$ . Dashed curves guide the eye. (c) Magnetic field dependence of the dielectric constant at various $T$ from Ref. 4.Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Coupling between magnon and ligand-field excitations in magnetoelectric ${Tb}_{3} {Fe}_{5} O_{12}$ garnet

T. D. Kang, E. Standard, K. H. Ahn, A. A. Sirenko, G. L. Carr, S. Park, Y. J. Choi, M. Ramazanoglu, V. Kiryukhin, and S.-W. Cheong

Phys. Rev. B 82, 014414 – Published 15 July 2010

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Physical Review B

covering condensed matter and materials physics

Coupling between magnon and ligand-field excitations in magnetoelectric Tb3Fe5O12 garnet

T. D. Kang, E. Standard, K. H. Ahn, A. A. Sirenko, G. L. Carr, S. Park, Y. J. Choi, M. Ramazanoglu, V. Kiryukhin, and S.-W. Cheong

Phys. Rev. B 82, 014414 – Published 15 July 2010

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Coupling between magnon and ligand-field excitations in magnetoelectric ${Tb}_{3} {Fe}_{5} O_{12}$ garnet