EPR studies of AsO4−4 spin-lattice-relaxation times in antiferroelectric NH4H2AsO4 and mixed glassy Rb1−x(NH4)xH2AsO4 (x=0.35)

Abstract

The electron spin-lattice-relaxation time T1 was measured for x-ray-induced AsO4−4 centers in antiferroelectric NH4H2AsO4 (ADA) and mixed Rb1−x(NH4)xH2AsO4 (RADA, x=0.35) in the temperature range 4.2–300 K by the saturation method. It is shown that below T0 1/T1 reflects the direct relaxation process. From above T0 to 55 K, 1/T1∝T1.6 and can be described by a Vogel-Fulcher law 1/T1∼(T-T0). It is also shown that the flatness of 1/T1 in the temperature region from 55 to 120 K is due to the tunneling motion of nitrogen in the glassy phase of RADA. Contrary to ADA, the 1/T1 behavior in RADA reflects the fracton nature of relaxation in the spin-glass state.