Frequency Dispersion of the Proton Zeeman Spin-lattice Relaxation in the Smectic Phases of Tbba

Using a field cycling technique, the Larmor frequency (VL) dependence of the proton Zeeman spin-lattice relaxation time T I has been measured in the smectic A, smectic C, smectic B and smectic VII phases of terephtal-bis-butylaniline (TBBA) between VL = 90 MHz and V L = 0.14 MHz and a significant dispersion has been found. The observed c o i J 2 dispersion law in the smectic A phase and the deviations from it at low frequencies can be explained by nematic director fluctuations in the smectic A phase and the coupling between nematic and smectic order. Whereas the nuclear spin-lattice relaxation mechanisms in nematic liquid crystals have been the subject of many investigations [l-61, very little is known about the nature of the spin-lattice relaxation process in smectic systems [3]. In this letter we report what we believe to be the first extended measurements of the Larmor frequency dependence of the proton spin-lattice relaxation time TI in the smectic A, smectic C, smectic B,(H) and smectic VII phases [7]. The system investigated was terephtal-bis-butyIaniline (TBBA). The results show that collective order fluctuations dominate the spin-lattice relaxation process in the smectic A phase and produce a characteristic frequency dispersion of TI. The measurements were performed in the magnetic field range between H = 21.4 kG