Regensburg 2016 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 78: Correlated Electrons: Poster Session

TT 78.2: Poster

Donnerstag, 10. März 2016, 15:00–18:30, Poster D

Dielectric and thermodynamic measurements on the magnetoelectric perovskite EuTiO₃ — •Johannes Engelmayer, Christoph Grams, Joachim Hemberger, and Thomas Lorenz — II. Physikalisches Institut, Universität zu Köln, Germany

Various perovskite titanates ATiO₃ are known to undergo ferroelectric phase transitions, e.g., for A=Ba,Pb,Cd. BaTiO₃ is the only ferroelectric alkaline-earth titanate, since ferroelectric long-range order is suppressed in CaTiO₃ and SrTiO₃ by quantum fluctuations, which is referred to as quantum paraelectric behavior. The rare-earth titanate EuTiO₃ is similar to SrTiO₃, since it has the same valencies (Eu²⁺,Ti⁴⁺) and the same ionic radii. Both are cubic at room temperature and undergo a structural phase transition to tetragonal upon cooling. In contrast to the nonmagnetic Sr²⁺, the half-filled 4f shell of Eu²⁺ with S=7/2 has a large magnetic moment of 7µ_B. Below T_N=5.5 K the localized 4f moments order antiferromagnetically, while rather small fields of 1.5 T are sufficient to saturate the magnetization. Here we present field- and temperature-dependent measurements of magnetization, specific heat, and thermal expansion, exhibiting characteristic anomalies at T_N. Broadband measurements of the permittivity reveal the dynamics of polar domain walls at the onset of the structural phase transition, as well as the materials quantum paraelectric nature that is masked by high conductivity for low frequencies.

This work has been supported by the DFG through the Institutional Strategy of the University of Cologne within the German Excellence Initiative.