Berlin 2012 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 13: Magnetic Materials

MA 13.9: Vortrag

Montag, 26. März 2012, 17:00–17:15, H 0112

Terahertz Spectroscopy of Overdoped Manganites — •F. Fischgrabe¹, V. Moshnyaga¹, T. Zhang², L. Kadyrov³, E. Zhukova^3,6, B. Gorshunov^3,6, V. Torgashev⁴, K. Velebit^5,6, U. Pracht⁶, and M. Dressel⁶ — ¹I. Physikalisches Institut, Universität Göttingen, Germany — ²Institute of Solid State Physics, Chinese Academy of Sciences, Hefei, China — ³Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow, Russia — ⁴Faculty of Physics, Southern Federal University, Rostov on Don, Russia — ⁵Institut of Physics, Zagreb, Croatia — ⁶I. Physikalisches Institut, Universität Stuttgart, Germany

Highly doped manganites La_1−xCa_xMnO₃ with the composition
0.5 < x < 1 are synthesized as ceramic samples and epitaxial films on MgO. Using a coherent source terahertz spectrometer, the dynamical conductivity and dielectric permittivity spectra are measured in the spectral range from 8 cm⁻¹ to 48 cm⁻1 and at temperatures from 5 K to 300 K. In the samples with x ≈ 0.5 an insulator to metal phase transition is seen while cooling below ≈80 K whose origin could be caused by coexistence of ferromagnetic metallic and anti-ferromagnetic insulator phases. For commensurate calcium contents (x=1/2, 2/3) strong resonances at terahertz frequencies are seen and ascribed to acoustic phonons that become optically active due to Brillouin zone folding accompanying changes in crystal lattice (as seen for x=3/4 in [1]). Incommensurate doping result in broad absorptions due to acoustic phonons density of states.
1. T. Zhang et al. Physical Review B 81, 125132 (2010).