Electron paramagnetic resonance governed by the Dzyaloshinsky-Moriya antisymmetric exchange interaction in CuGeO₃

Several reports of electron paramagnetic resonance experiments performed on the spin-Peierls compound CuGeO₃ have appeared so far, but none of them have precisely explained the origin of the line broadening and the temperature dependence of both the linewidth and the resonance field, all of which differ from those of conventional one-dimensional Heisenberg antiferromagnets in which the dipolar or anisotropic exchange interaction brings about line broadening. In the present report, it is clarified that the antisymmetric exchange interaction, Σ_i d_ii+1 · (S_i × S_i+1) with d_ii+1 ⊥ c-axis (magnetic chain), between nearest-neighbour Cu spins on the c-axis governs all factors which characterize the EPR line of CuGeO₃, i.e., the value and the angular dependence of the linewidth at high temperatures where the short-range order is completely absent, the temperature dependence of the linewidth, and the resonance field, as well as the high-temperature lineshape. The present conclusion indicates that the crystal symmetry of this compound is lower than that given by the space group Pbmm which was reported by Völlenkle et al in 1967, because the symmetry Pbmm does not allow the antisymmetric exchange interaction mentioned above.