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Berlin 2008 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 4: Matter at Low Temperature: Materials

TT 4.3: Talk

Monday, February 25, 2008, 10:15–10:30, H 3010

Structural phase transition in CdCr2O4 probed by far-infrared spectroscopy — •Torsten Rudolf1, Christian Kant1, Joachim Deisenhofer1, Franz Mayr1, Vladimir Tsurkan1,2, and Alois Loidl11Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, D-86135 Augsburg, Germany — 2Institute of Applied Physics, Academy of Sciences of Moldova, MD-2028 Chişinǎu, Republic of Moldova

Strongly frustrated single crystalline CdCr2O4 [1] was investigated by means of Fourier Transform infrared spectroscopy. The temperature dependence of the far-infrared phonon spectrum was studied from 5 to 300 K. The space group of CdCr2O4 at room temperature is Fd3m and group theory predicts four infrared active phonon modes, which is verified by experiment. The formation of a pyrochlore lattice by the chromium ions leads to a strong geometric frustration in this spinel system, represented by a high frustration parameter f≈ 9. It is examined whether below the Néel temperature TN the magnetic ground state degeneracy is rather lifted by a lattice distortion or by a magnetic exchange induced symmetry breaking. However, due to a strong spin-phonon coupling each single phonon mode shows a splitting below TN ≈ 8 K. At 5 K the reflectivity data can be fitted with nine phonons via a generalized oscillator model using four parameters per mode. Dielectric loss data, calculated via the Kramers-Kronig transformation, even uncover a splitting into more than nine phonon modes.
T. Rudolf et al., New J. Phys. 9, 76 (2007)

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