Spin-phonon coupling in multiferroic manganites RMnO3: comparison of pure (R = Eu, Gd, Tb) and substituted (R = Eu1-xYx) compounds

• Published in: The European physical journal. B, Condensed matter physics Vol. 78; no. 3; pp. 367 - 372
• Main Authors: Issing, S., Pimenov, A., Ivanov, Y. Vu, Mukhin, A. A., Geurts, J.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01-12-2010
• Subjects: Complex Systems; Condensed Matter Physics; Fluid- and Aerodynamics; Physics; Physics and Astronomy; Solid State Physics; Manganite; Sublattice Magnetization; Phonon Frequency; Orthorhombic Distortion; Phonon Mode
• ISSN: 1434-6028; 1434-6036
• DOI: 10.1140/epjb/e2010-10701-0

For rare-earth manganite RMnO
3
compounds spin-phonon coupling manifests itself as a phonon softening in the temperature range of the magnetically ordered phases. Within this class of materials, a continuous tuning of the lattice and thus also of the magnetic properties of multiferroic manganites is achieved by Y doping in substituted Eu
1-
x
Y
x
MnO
3
. We compare the impact on spin-phonon coupling within this partial-substitution approach in a series of Eu
1-
x
Y
x
MnO
3
samples 0
≤
x
≤
0.5) with the effect of a complete exchange of the rare earth ions R
3+
in a series of pure RMnO
3
compounds (R = Eu, Gd, Tb). For this purpose we employ polarized Raman scattering in the 10–300 K temperature range. The low-temperature results show phonon softening in all investigated compounds. For decreasing R
3+
radius, i.e. an increasing orthorhombic distortion and magnetic frustration, we observe in both systems a weakening of the spin-phonon coupling. For known sublattice magnetization within the MnO
2
-plane, quantitative results for the spin-phonon coupling constant are derived for both cases within a molecular field approximation. Our results show, that the spin-phonon coupling strength in the magnetically ordered phases of the various investigated manganites does not correlate with the magnetization pattern. Instead, the pure RMnO
3
compounds and the substituted Eu
1-
x
Y
x
MnO
3
fit excellently within a common scheme, in which the weakening of the spin-phonon coupling reflects the degree of tilting of the MnO
6
octahedra due to the orthorhombic distortion of the crystal lattice.