MAGNETIC ORDERING IN CU2CS3CL7.2H2O SINGLE CRYSTALS STUDIED BY NUCLEAR MAGNETIC RESONANCE

The frequency shifts of the proton resonance lines of Cu2Cs3Cl7.2H2O as well as their linewidths have been measured in the paramagnetic and antiferromagnetic state. In the paramagnetic state a strong one-dimensional short range interaction between the cupric spins exists, leading to an ordering in linear chains. The measured susceptibility is compared with the calculations by Bonner and Fisher for the zero-field susceptibility of an infinite chain of antiferromagnetically isotropic coupled spins. The resonance linewidth increases to lower temperatures, similar to the line broadening found in CuSo4.5H2O. Just above the transition temperature to the ordered state (TN ≈ 1.62 K) a sharp decrease of the linewidth appears instead of an increase as predicted among others by Moriya. Just below the Néel point the temperature dependence of the sublattice magnetization shows a deviation from that found in most other antiferromagnets. The critical increase in linewidth in the antiferromagnetic state when the Néel temperature is approached is in qualitative agreement with the calculations of Moriya. To obtain information about the contribution of the inhomogeneous broadening due to a spread in TN we measured the broadening in several crystals. © 1969.