Regensburg 2016 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 77: Multiferroics
(Joint session of MA, DF, DS, KR and TT organized by MA)
TT 77.2: Vortrag
Donnerstag, 10. März 2016, 15:15–15:30, H34
Multiferroic vs. magnetoelectric properties of the dilution series [(NH4)1−xKx]2[FeCl5(H2O)] — •Daniel Brüning1, Matthias Ackermann1, Ladislav Bohaty2, Petra Becker2, and Thomas Lorenz1 — 1II. Physikalisches Institut, Universität zu Köln, Germany — 2Insitut für Kristallographie, Universität zu Köln, Germany
Recently we found that (NH4)2[FeCl5(H2O)], a member of the antiferromagnetic erythrosiderites A2[FeX5(H2O)] (A = K, Rb, Cs or NH4 and X = Cl or Br) is multiferroic with a spontaneous polarization at TC= 6.87K, slightly below the magnetic ordering at TN= 7.25K. Additionally we found a high-temperature structural phase transition Tst= 79K, related to a monoclinic distortion (Pnma to P112/a) due to a rearrangement of the hydrogen atoms. In contrast to (NH4)2[FeCl5(H2O)], the related erythrosiderites with A = K, Rb or Cs are not multiferroic, but show linear magnetoelectric coupling with Pi = αijHj below TN. Investigating the dilution series with A = (NH4)1−xKx provides information on the stability of the multiferroic versus magnetoelectric behavior. Based on dielectric and magnetic measurements we present detailed magnetic-field versus temperature phase diagrams. Interestingly, the mixed crystals develop a finite pyroelectric polarization at Tst, whereas there is no indication of pyroelectricity above TN, neither in the pure (NH4)-based nor in the pure K-based compound.
M. Ackermann et al., J. Phys.: Condens. Matter, 26, 506002, (2014)
M. Ackermann et al., New J. Phys., 15 123001, (2013)