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 mod el with nearest-(J(1)) and next-nearest-neighbor interactions (J(2)) W e show that the ratio of the exchange constants in the antiferromagnet ic chains of CuGeO3, amounts to J(2)/J(1) = 0.354(0.01), i.e, it is si gnificantly larger than the critical value for the formation of a spon taneous gap in the magnetic excitation spectrum without lattice dimeri zation. The susceptibility data are reproduced by our numerical result s over the temperature range from 20 to 950 K to a high degree of accu racy for J(1) = 80.2(3.0) and J(2) = 28.4(1.8). The pressure dependenc e of the exchange constants is estimated from magnetostriction data. F urthermore. the specific-heat data an checked for consistency against the calculated entropy of the above model.