Reexamination of the microscopic couplings of the quasi one-dimensional antiferromagnet CuGeO_3

TL;DR

This paper reexamines the magnetic couplings in CuGeO_3, showing that its exchange interactions are larger than previously thought, and provides a detailed analysis of susceptibility, magnetostriction, and specific heat data within a one-dimensional antiferromagnetic model.

Contribution

It offers a revised estimate of the exchange constants in CuGeO_3 and demonstrates the model's accuracy across a wide temperature range, including pressure effects.

Findings

The ratio J_2/J_1 is approximately 0.354, indicating strong next-nearest neighbor interactions.

Numerical susceptibility results match experimental data from 20K to 950K.

Pressure dependence of exchange constants is estimated from magnetostriction data.

Abstract

Experimental data for the magnetic susceptibility and magnetostriction of CuGeO_3 are analyzed within a one-dimensional antiferromagnetic model with nearest ({J_1}) and next-nearest neighbour interactions ({J_2}). We show that the ratio of the exchange constants in the antiferromagnetic chains of CuGeO_3 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 20K to 950K 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 are checked on consistency against the calculated entropy of the above model.