Europhys. Lett.
Volume 75, Number 3, August 2006
Page(s) 496 - 502
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 30 June 2006
Europhys. Lett., 75 (3), pp. 496-502 (2006)
DOI: 10.1209/epl/i2005-10603-3

Optical evidence for a magnetically driven structural transition in the spin web $\rm Cu_3TeO_6$

G. Caimi1, L. Degiorgi1, H. Berger2 and L. Forró2

1  Laboratorium für Festkörperphysik, ETH Zürich - CH-8093 Zürich, Switzerland
2  Institut de Physique de la Matière Complexe (IPMC), EPF Lausanne CH-1015 Lausanne, Switzerland

received 30 November 2005; accepted in final form 9 June 2006
published online 30 June 2006

Cu3TeO6 is a modest frustrated S=1/2 spin system, which undergoes an antiferromagnetic transition at $T_N \sim 63$ K. The antiferromagnetic spin alignment in Cu3TeO6 below TN is supposed to induce a magneto-elastic strain of the lattice. The complete absorption spectrum of Cu3TeO6 is obtained through Kramers-Kronig transformation of the optical reflectivity, measured from the far-infrared up to the ultraviolet spectral range as a function of temperature (T). Below $T^*\sim 50$ K, we find a new mode at 208 cm-1. The spectral weight associated to this additional mode increases as $\propto (T^*-T)^{1/2}$ with decreasing T below T*. The implication of the optical findings will be discussed in relation to the magnetic phase transition at TN.

78.20.-e - Optical properties of bulk materials and thin films.
75.50.Ee - Antiferromagnetics.
75.30.Gw - Magnetic anisotropy.

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