Europhys. Lett.
Volume 70, Number 3, May 2005
Page(s) 369 - 375
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 13 April 2005
Europhys. Lett., 70 (3), pp. 369-375 (2005)
DOI: 10.1209/epl/i2004-10499-3

Anisotropic spin-Peierls state in the inorganic compound $\chem{CuGeO_3}$

M. Miljak1, M. Herak1, A. Revcolevschi2 and G. Dhalenne2

1  Institute of Physics - Bijenicka c. 46, 10000 Zagreb, Croatia
2  Laboratoire de Phisico-Chimie de l'Etat Solide, Université de Paris Sud Bâtiment 414, 91405 Orsay, France

received 6 July 2004; accepted in final form 15 March 2005
published online 13 April 2005

The static susceptibility and susceptibility anisotropy of the single-crystalline $\chem{CuGeO_3}$ were measured. Combined results of both techniques reveal the following experimental facts: i) The low-temperature susceptibility upturn obeys a power law temperature dependence of the $A\;T^{-\alpha}$ form with $\alpha$ an anisotropic exponent. This is, to our knowledge, the first observation of the anisotropic exponent $\alpha$. ii) In the paramagnetic region above the spin-Peierls transition temperature the measurements reveal the anisotropic and temperature-dependent exchange interaction, J. iii) The anisotropic exchange interaction results in the anisotropy of the excitation energy gap $\Delta$. iv) The paramagnetic defects causing a low-temperature susceptibility upturn are $\chem{Cu^{2+}}$ ions, but of different oxygen surroundings than the rest of the $\chem{Cu^{2+}}$ moments.

75.30.Gw - Magnetic anisotropy.
75.30.Hx - Magnetic impurity interactions.
75.30.Et - Exchange and superexchange interactions.

© EDP Sciences 2005