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arXiv · 1705.02143

Unusual ferroelectric and magnetic phases in multiferroic 2H-BaMnO$_3$ ceramics

Stanislav Kamba·Dmitry Nuzhnyy·Maxim Savinov·Pierre Toledano·Valentin Laguta·Petr Brazda·Lukas Palatinus. Filip Kadlec·Fedir Borodavka·Christelle Kadlec·Petr Bednyakov·Viktor Bovtun·Martin Kempa·Dominik Kriegner·Jan Drahokoupil·Jan Kroupa·Jan Prokleska·Kamal Chapagain·Bogdan Dabrowski·Veronica Goian
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Abstract

The structural phase transition in hexagonal BaMnO$_3$ occurring at $T_c$=130 K was studied in ceramic samples using electron and X-ray diffraction, second harmonic generation as well as by dielectric and lattice dynamic spectroscopies. The low-temperature phase (space group $P6_{3}cm$) is ferroelectric with a triplicated unit cell. The phase transition is driven by an optical soft mode from the Brillouin-zone boundary [$q = (\frac{1}{3},\frac{1}{3},0)$]; this mode activates in infrared and Raman spectra below $T_c$ and it hardens according to the Cochran law. Upon cooling below $T_c$, the permittivity exhibits an unusual linear increase with temperature; below 60 K, in turn, a frequency-dependent decrease is observed, which can be explained by slowing-down of ferroelectric domain wall motions. Based on our data we could not distinguish whether the high-temperature phase is paraelectric or polar (space groups $P6_{3}/mmc$ or $P6_{3}mc$, respectively). Both variants of the phase transition to the ferroelectric phase are discussed based on the Landau theory. Electron paramagnetic resonance and magnetic susceptibility measurements reveal an onset of one-dimensional antiferromagnetic ordering below $\approx220\,\rm K$ which develops fully near 140 K and, below $T_{n} \approx 59\,\rm K$, it transforms into a three-dimensional antiferromagnetic order.

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Stanislav Kamba, Dmitry Nuzhnyy, Maxim Savinov, Pierre Toledano, Valentin Laguta, Petr Brazda, Lukas Palatinus. Filip Kadlec, Fedir Borodavka, Christelle Kadlec, Petr Bednyakov, Viktor Bovtun, Martin Kempa, Dominik Kriegner, Jan Drahokoupil, Jan Kroupa, Jan Prokleska, Kamal Chapagain, Bogdan Dabrowski, Veronica Goian. 2017-05-05. Unusual ferroelectric and magnetic phases in multiferroic 2H-BaMnO$_3$ ceramics. https://doi.org/10.1103/physrevb.95.174103

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