Thermal hysteresis in TlH ₂AsO ₄ studied by ¹H NMR

The ferroelastic phase of TlH ₂AsO ₄ (TDA) was investigated by means of ¹H nuclear magnetic resonance (NMR) at the Larmor frequencies of 13.5 MHz and 45 MHz. At both frequencies, the nuclear magnetization recovery was well fitted by the stretched-exponential function, M (t)=M ₀[1 - exp[-(t/T ₁) ^1-n]], with the spin-lattice relaxation times exhibiting thermal hysteresis. The thermal hysteresis was quite pronounced at 13.5 MHz, where the ¹H NMR- ⁷⁵As NQR cross relaxation was observed in the temperature range studied in this work. Our results are discussed in the light of the ferroelastic glass-like nature in the ferroelastic phase of TDA.