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Infrared and THz studies of polar phonons and improper magnetodielectric effect in multiferroic BFO3 ceramics

S. Kamba·D. Nuzhnyy·M. Savinov·J. Sebek·J. Petzelt·J. Prokleska·R. Haumont·J. Kreisel
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Abstract

BFO3 ceramics were investigated by means of infrared reflectivity and time domain THz transmission spectroscopy at temperatures 20 - 950 K, and the magnetodielectric effect was studied at 10 - 300 K, with the magnetic field up to 9 T. Below 175 K, the sum of polar phonon contributions into the permittivity corresponds to the value of measured permittivity below 1 MHz. At higher temperatures, a giant low-frequency permittivity was observed, obviously due to the enhanced conductivity and possible Maxwell-Wagner contribution. Above 200 K the observed magnetodielectric effect is caused essentially through the combination of magnetoresistance and the Maxwell-Wagner effect, as recently predicted by Catalan (Appl. Phys. Lett. 88, 102902 (2006)). Since the magnetodielectric effect does not occur due to a coupling of polarization and magnetization as expected in magnetoferroelectrics, we call it improper magnetodielectric effect. Below 175 K the magnetodielectric effect is by several orders of magnitude lower due to the decreased conductivity. Several phonons exhibit gradual softening with increasing temperature, which explains the previously observed high-frequency permittivity increase on heating. The observed non-complete phonon softening seems to be the consequence of the first-order nature of the ferroelectric transition.

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S. Kamba, D. Nuzhnyy, M. Savinov, J. Sebek, J. Petzelt, J. Prokleska, R. Haumont, J. Kreisel. 2006-11-09. Infrared and THz studies of polar phonons and improper magnetodielectric effect in multiferroic BFO3 ceramics. https://doi.org/10.1103/physrevb.75.024403

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