New phase transition studied by proton magnetic resonance in a [N(CH3)4]2CuCl4 single crystal

The proton NMR line width and spin–lattice relaxation rate in a [N(CH3)4]2CuCl4 single crystal have been investigated in the temperature range of 140–340 K. A large discontinuity in the curve of the spin–lattice relaxation rate shows near 200 K: this curve corresponds to a new phase transition. The activation energies were determined at each phase from the spin–lattice relaxation times. The large change in the activation energy at 200 K indicates that the N(CH3)4 groups are significantly affected during this transition.