CU-63,CU-65 NMR AND NQR STUDY OF THE CU2+ ELECTRONIC-STATE AND THE SPIN DYNAMICS IN THE SPIN-PEIERLS COMPOUND CUGEO3

Cu-63,Cu-65 NMR and NQR measurements have been performed to study the Cu2+ electronic state and the spin dynamics in CuGeO3, which is an inorganic compound that undergoes the spin-Peierls transition at T-sp similar to 14 K. The NQR frequency is discussed in connection with the lattice dimerization accompanied by the spin-Peierls transition. The Knight shift with an axial symmetry showed the temperature dependence corresponding to the reduction of the spin susceptibility. From the analysis of the Knight shift and the magnetic susceptibility, orbital and spin susceptibilities are evaluated. The analysis of the hyperfine structure leads to a conclusion that the electronic state of the Cu2+ ion above T-sp is described by a single-ion model in a crystal field with a tetragonal symmetry. The supertransferred hyperfine interaction, which is one of the characteristic features of Cu2+ ions in the CuO2 plane in the high-T-c superconducting copper oxides, is found not to play an important role in CuGeO3. The temperature dependence of the nuclear spin-lattice relaxation rate 1/T-1 clearly shows presence of a gap in the magnetic excitation spectrum below T-sp. The relaxation mechanism is discussed based on the spinless fermion treatment for an S = 1/2 one-dimensional Heisenberg antiferromagnet (1DHAF) above T-sp and for a nonuniform S = 1/2 1DHAF with two unequal and alternating exchange interactions below T-sp. Above T-sp, it is also discussed in terms of the dynamical susceptibility of the 1DHAF.