Polar phonon mixing in magnetoelectric EuTiO3 |
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| Authors: | V Goian S Kamba J Hlinka P Vaněk A A Belik T Kolodiazhnyi and J Petzelt |
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| Institution: | (1) Institute of Physics ASCR, Na Slovance 2, 18221 8 Prague, Czech Republic;(2) Ceramics Laboratory, Swiss Federal Institute of Technology, EPFL, CH-1015 Lausanne, Switzerland;(3) Microelectronics and Materials Physics Laboratories, and EMPART Research Group of Infotech Oulu, University of Oulu, PL 4500, Oulun Yliopisto, 900014 Oulu, Finland |
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| Abstract: | Infrared reflectivity spectra of antiferromagnetic incipient ferroelectric
EuTiO3 were investigated up to 600 K. Three polar phonons typical for
the cubic perovskite Pm`3]mPm\bar {3}m structure were observed. Analysis of
phonon plasma frequencies showed that the lowest-energy TO1 phonon
corresponds predominantly to the Slater mode describing vibration of Ti
cations against the oxygen octahedra and the TO2 phonon expresses vibrations
of the Eu cation against the TiO6 octahedra. The highest frequency TO4
phonon represents O-octahedra bending. Incipient ferroelectric behavior of
the permittivity is caused by pronounced softening of the TO1 phonon, which
is coupled to the TO2 mode. Although the Eu cations are not involved in the
TO1 mode, the spin ordering of the 4f electrons at Eu cations has influence
on the frequency of the TO1 mode due to Eu-O-Eu super-exchange interaction.
This is probably responsible for the 7% change of the permittivity
induced by the magnetic field in the antiferromagnetic phase, as reported by
Katsufuji and Takagi Phys. Rev. B 64, 054415 (2001)]. |
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