Regensburg 2007 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 4: Solids at Low Temperature - Materials
TT 4.2: Vortrag
Montag, 26. März 2007, 11:45–12:00, H18
Spin-phonon coupling in chromium spinels probed by infrared spectroscopy — •Torsten Rudolf1, Christian Kant1, Franz Mayr1, Joachim Hemberger1, 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 Chisinau, Republic of Moldova
The B-site spinels ACr2X4 with A=Cd, Zn, Hg and X=S, O and Se were systematically investigated by Fourier Transform Infrared Spectroscopy. The temperature and magnetic field dependence of the phonon spectra in a range
from 5 K to 300 K and in fields of up to 7 T where studied. At the magnetic ordering temperature most compounds show significant splittings of the phonon modes, driven by spin-phonon coupling. CdCr2O4 and ZnCr2O4 are geometrically frustrated, ZnCr2S4 [1] is bond frustrated and ZnCr2Se4 [2] is bond frustrated, but dominated by ferromagnetic exchange. The pattern of splittings is different for the different compounds and crucially depends on the nature of frustration and of the resulting spin order. HgCr2S4 is almost a ferromagnet and exhibits no splitting of the eigenfrequencies, whereas ZnCr2Se4 is a prominent example of a spin-driven Jahn-Teller effect, where the splitting of the low-energy phonon
mode can be fully suppressed in an external magnetic field.
J. Hemberger et al., Phys. Rev. Lett. 97, 087204 (2006)
T. Rudolf et al., Spin-phonon coupling in ZnCr2Se4, Preprint cond-mat/0611041