Abstract
The static susceptibility and susceptibility anisotropy of the single-crystalline CuGeO3 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−α form with α an anisotropic exponent. This is, to our knowledge, the first observation of the anisotropic exponent α. 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 Δ. iv) The paramagnetic defects causing a low-temperature susceptibility upturn are Cu2+ ions, but of different oxygen surroundings than the rest of the Cu2+ moments.