ROTATING-FRAME NUCLEAR MAGNETIC-RELAXATION IN TLH2PO4

A TlH2PO4 single crystal was studied by means of the rotating-frame NM R measurements and the results were compared with our recent work on a TlH2AsO4 polycrystalline sample. When the data were fitted in the sam e manner, similar overall features were observed, whereas anomalies at the antiferroelectric phase transition were much more pronounced. On the other hand, a double-exponential fit at all temperatures suggests that both of the domain structures participate in the antiferroelectri c phase transition, whereas only one of them undergoes the ferroelasti c phase transition. The domain structure that does not undergo the fer roelastic phase transition shows a differential anomaly in the spin-la ttice relaxation at the critical temperature, which appears to be char acteristic of an order-disorder transition.