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Unusual ferroelectric and magnetic phases in multiferroic 2H−BaMnO3 ceramics

Stanislav Kamba1, Dmitry Nuzhnyy1, Maxim Savinov1, Pierre Tolédano2, Valentin Laguta1, Petr Brázda1, Lukáš Palatinus1, Filip Kadlec1, Fedir Borodavka1, Christelle Kadlec1, Petr Bednyakov1, Viktor Bovtun1, Martin Kempa1, Dominik Kriegner3, Jan Drahokoupil1, Jan Kroupa1, Jan Prokleška3, Kamal Chapagain4, Bogdan Dabrowski4, and Veronica Goian1

The structural phase transition in hexagonal BaMnO3 occurring at TC=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 P63cm) is ferroelectric with a triplicated unit cell. The phase transition is driven by an optical soft mode from the Brillouin-zone boundary [q=(1/3,1/3,0)]; this mode activates in infrared and Raman spectra below TC and it hardens according to the Cochran law. Upon cooling below TC, 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.

Temperature dependence of (a) dielectric permittivity and (b) dielectric loss of 2H−BaMnO3 ceramics measured at various frequencies. The values of tan δ at 6 GHz in the temperature interval between 30 and 90 K are missing due to high losses.

1Institute of Physics, Czech Academy of Sciences, Na Slovance 2, 182 21 Prague 8, Czech Republic
2Laboratoire de Physique de Systemes complexes, Université de Picardie, 80000 Amiens, France
3Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague 2, Czech Republic
4Department of Physics, Northern Illinois University, DeKalb, Illinois, USA