Phonon processes and the spin–lattice relaxation of two inequivalent Cs sites in Cs2CuCl4 and Cs2CoCl4 single crystals

The nuclear spin–lattice relaxation rates for 133Cs nucleus in Cs2CuCl4 and Cs2CoCl4 single crystals grown using the slow evaporation method were measured as a function of temperature. Two groups of 133Cs resonance lines for both crystals are obtained. They are due to the two crystallographically inequivalent types of 133Cs nuclei, Cs(I) and Cs(II). The inversion recovery trace of the central line of 133Cs was represented by a linear combination of four exponential functions. Thus, the relaxation behaviors of Cs(I) and Cs(II) in Cs2CuCl4 and Cs2CoCl4 single crystals are best explained by the T 1 − 1 = γ T + δ , and have spin–lattice relaxation rates in the slow region. We concluded that the relaxation behaviors of Cs(I) and Cs(II) in these crystals can be explained by a direct single-phonon process. The spin–lattice relaxation behaviors were quite similar for both crystals and were dominated by the phonon mechanism. These facts indicate that the Cs2CuCl4 and Cs2CoCl4 single crystals have the same A2BX4 structure, and their dynamic properties, such as their nucleus phonon interactions, are similar.