Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 4: Matter at Low Temperature: Materials
TT 4.3: Vortrag
Montag, 25. Februar 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 Loidl1 — 1Experimental 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)