Infrared-active phonon modes in monoclinic multiferroic MnWO4

Abstract

We report on polarized infrared reflectivity measurements of multiferroic, monoclinic MnWO4 between 10K and 295K. The full dielectric tensor and the frequency dependence of the orientation of the principal axes have been determined in the frequency range of the phonons. All infrared-active phonon modes (7 A_u modes and 8 B_u modes) are unambiguously identified. In particular the strongest B_u modes have been overlooked in previous studies, in which the monoclinic symmetry was neglected in the analysis. Using a generalized Drude-Lorentz model, we determine the temperature dependence of the phonon parameters, including the orientation of the B_u modes within the ac plane. The phonon parameters and their temperature dependence have been discussed controversially in previous studies, which do not include a full polarization analysis. Our data does not confirm any of the anomalies reported above 20K. However, in the paramagnetic phase we find a drastic reduction of the spectral weights of the weakest A_u mode and of the weakest B_u mode with increasing temperature. Below 20K, the parameters of the A_u phonon modes for E||b show only subtle changes, which demonstrate a finite but weak coupling between lattice dynamics and magnetism in MnWO4. A quantitative comparison of our infrared data with the quasi-static dielectric constant epsilon_b indicates that the spectral weight of the electromagnon is tiny for E||b, in particular much smaller than the weak changes of the spectral weight of the phonons.

published version, minor changes, 1 figure revised, 16 pages, 15 figures

References in corpus (20)

• Spin current and magneto-electric effect in non-collinear magnets
• Role of the Dzyaloshinskii-Moriya interaction in multiferroic perovskites
• Ferroelectric polarization flop in a frustrated magnet MnWO${}_4$ induced by magnetic fields
• Pressure effects on the structural and electronic properties of ABX4 scintillating crystals
• Dynamical magneto-electric coupling in helical magnets
• Origin of electromagnon excitations in \textit{R}MnO${}_3$
• A New Multiferroic Material: MnWO4
• Magnetic-induced phonon anisotropy in ZnCr${}_2$O${}_4$ from first principles
• Coupling of phonons and electromagnons in GdMnO_3
• Colossal magnon-phonon coupling in multiferroic Eu${}_{0.75}$Y${}_{0.25}$MnO${}_3$
• Long-Range Magnetic Interactions in the Multiferroic Antiferromagnet $\mathrm{MnW}{\mathrm{O}}_4$
• IR Phonon signatures of multiferroicity in TbMn${}_2$O${}_5$
• Modeling and Analysis Generic Interface for eXternal numerical codes (MAGIX)
• A simple prescription for simulating and characterizing gravitational arcs
• Polar phonons and spin-phonon coupling in HgCr2S4 and CdCr2S4
• Thermal expansion and pressure effect in MnWO4
• Origin of Multiferroicity in MnWO4
• Electronic structure and anomalous band-edge absorption feature in multiferroic MnWO4: An optical spectroscopic study
• Infrared reflectivity of the phonon spectra in multiferroic TbMnO3
• Soft-mode behavior of electromagnons in multiferroic manganite

Cited by in corpus (2)

• Critical slowing down near the multiferroic phase transition in MnWO${}_4$
• Electromagnon in the Z-type hexaferrite $({\mathrm{Ba}}_x{\mathrm{Sr}}_{1-x}{)}_3\mathrm{C}{\mathrm{o}}_2\mathrm{F}{\mathrm{e}}_{24}{\mathrm{O}}_{41}$