MAGNETOSTRICTION OF THE SPIN-PEIERLS COMPOUND CUGEO3

The longitudinal and transverse magnetostriction lambda of the spin-Pe ierls compound CuGeO3 in the b-c plane is measured in magnetic fields up to 20 T both above and below the transition temperature T-sp = 14.3 K. It is found that for a given crystallographic direction the value o f magnetostriction is weakly dependent on the magnetic field direction . In the uniform U phase at T greater than or equal to T-sp, lambda is negative and approximately equal in the b and c directions, while in the dimerized D phase at T < T-sp, lambda is positive and lambda(b) > lambda(c). At low temperatures, lambda increases sharply at the magnet ic-field-induced transition from the dimerized to the magnetic M phase . The experimental data allow estimation of the stress derivatives of the antiferromagnetic intrachain exchange interaction parameter and of the stress dependence of the critical field of the D-M phase transiti on. (C) 1996 American Institute of Physics.