The 1H chemical shifts and the spin-lattice relaxation time, T1ρ, in the rotating frame of (NH4)2ZnX4 (X = Cl, Br) are observed in order to investigate local phenomena related to successive phase transitions. The temperature dependence of T1ρ values for 1H showed a minimum, and the T1ρ values for 1H appeared to be governed by tumbling molecular motions at high temperatures. In addition, 14N NMR spectra are studied in each phase of (NH4)2ZnX4 single crystals in the laboratory frame. The phase transition temperatures strongly affect the 14N number of symmetry related nitrogen centers within the unit cell. The 1H MAS NMR and 14N NMR results are discussed to elucidate the roles of NH4 ions during the phase transitions of (NH4)2ZnX4.
