Reexamination of the microscopic couplings of the quasi-one-dimensional antiferromagnet CuGeO3

Experimental data for the magnetic susceptibility and magnetostriction of CuGeO3 are analyzed within a one-dimensional antiferromagnetic model with nearest-(J(1)) and next-nearest-neighbor interactions (J(2)) We show that the ratio of the exchange constants in the antiferromagnetic chains of CuGeO3, amounts to J(2)/J(1) = 0.354(0.01), i.e, it is significantly larger than the critical value for the formation of a spontaneous gap in the magnetic excitation spectrum without lattice dimerization. The susceptibility data are reproduced by our numerical results over the temperature range from 20 to 950 K to a high degree of accuracy for J(1) = 80.2(3.0) and J(2) = 28.4(1.8). The pressure dependence of the exchange constants is estimated from magnetostriction data. Furthermore. the specific-heat data an checked for consistency against the calculated entropy of the above model.