Regensburg 2007 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 15: Poster:ThinFilms(1-33),Transp.(34-49),ExchBias(50-56),
Spindynamics(57-70),Micro-nanostr.Mat.(71-82),
Particles/Clust.(83-88), Mag.Imag./Surface(89-96),
Spinelectronics(97-109), Theory/Micromag.(110-116),
Spinstruct/Phasetr.(117-128),Magn.Mat.(129-139),
Aniso.+Measuring(140-145), MolMag.(146-152),
MSMA(153-156)

MA 15.118: Poster

Dienstag, 27. März 2007, 15:00–19:00, Poster A

Thermal Expansion and Thermal Transport in NdMnO₃ and TbMnO₃ — •Kai Berggold¹, Thomas Lorenz¹, Jörg Baier¹, John Mydosh¹, Dennis Meier², Joachim Hemberger³, and Dimitri Argyriou⁴ — ¹II. Physikalisches Institut, University of Cologne, Germany — ²Helmholtz - Inst. f. Strahlen und Kernphysik, University of Bonn, Germany — ³Inst. f. Physik, University of Augsburg, Germany — ⁴Hahn-Meitner-Institut, 14109 Berlin, Germany

We present measurements of the thermal expansion α and the thermal conductivity κ of NdMnO₃ and TbMnO₃. NdMnO₃ is an A type antiferromagnet with T_N=88 K, whereas TbMnO₃ is known for its multiferroic properties, leading to complex magnetic and electric ordering phenomena at low temperatures. In NdMnO₃, the Néel transition causes large anomalies in α as well as in κ. At low temperatures the crystal-field splitting of the Nd³⁺ ground state causes a Schottky-type contribution to the thermal expansion. The thermal conductivity at low temperatures is strongly suppressed by this splitting, as a consequence of resonant phonon-scattering processes. In TbMnO₃, we show that the main factor determining κ is also given by resonant scattering between different crystal-field split states of the 4f multiplet of the Tb³⁺ ions. In contrast to NdMnO₃, the suppression acts in a much wider temperature range. The various transitions at low temperatures observed by anomalies of the thermal expansion have no significant influence on the thermal conductivity.

Supported by the DFG through SFB 608