Berlin 2012 – scientific programme
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MA: Fachverband Magnetismus
MA 13: Magnetic Materials
MA 13.9: Talk
Monday, March 26, 2012, 17:00–17:15, H 0112
Terahertz Spectroscopy of Overdoped Manganites — •F. Fischgrabe1, V. Moshnyaga1, T. Zhang2, L. Kadyrov3, E. Zhukova3,6, B. Gorshunov3,6, V. Torgashev4, K. Velebit5,6, 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 La1−xCaxMnO3 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).