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arXiv · 1110.0473

Raman scattering study of delafossite magnetoelectric multiferroic compounds: CuFeO2 and CuCrO2

O. Aktas·K. D. Truong·T. Otani·G. Balakrishnan·M. J. Clouter·T. Kimura·G. Quirion
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Abstract

Ultrasonic velocity measurements on the magnetoelectric multiferroic compound CuFeO2 reveal that the antiferromagnetic transition observed at TN1 = 14 K might be induced by an R-3m -> C2/m pseudoproper ferroelastic transition (G. Quirion, M. J. Tagore, M. L. Plumer, O. A. Petrenko, Phys. Rev. B 77, 094111 (2008)). In that case, the group theory states that the order parameter associated with the structural transition must belong to a two dimensional irreducible representation Eg (x^2 - y^2, xy). Since this type of transition can be driven by a Raman Eg mode, we performed Raman scattering measurements on CuFeO2 between 5 K and 290 K. Considering that the isostructural multiferroic compound CuCrO2 might show similar structural deformations at the antiferromagnetic transition TN1 = 24.3 K, Raman measurements have also been performed for comparison. At ambient temperature, the Raman modes in CuFeO2 are observed at omega_Eg = 352 cm^-1 and omega_Ag = 692 cm^-1, while these modes are detected at omega_E_g = 457 cm^-1 and omega_Ag = 709 cm^-1 in CuCrO2. The analysis of the temperature dependence of modes shows that the frequency of all modes increases down to 5 K. This typical behavior can be attributed to anharmonic phonon-phonon interactions. These results clearly indicate that none of the Raman active modes observed in CuFeO2 and CuCrO2 drive the pseudoproper ferroelastic transition observed at the Néel temperature TN1. Finally, a broad band at about 550 cm^-1 observed in the magnetoelectric phase of CuCrO2 below TN2 could be attributed to a magnon mode.

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O. Aktas, K. D. Truong, T. Otani, G. Balakrishnan, M. J. Clouter, T. Kimura, G. Quirion. 2011-10-03. Raman scattering study of delafossite magnetoelectric multiferroic compounds: CuFeO2 and CuCrO2. https://doi.org/10.1088/0953-8984%2F24%2F3%2F036003

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