ALTERNATING-CURRENT SUSCEPTIBILITY STUDIES OF TB ORDERING IN PB2SR2TBCU3O8

The magnetic response of the Tb spins in Pb2Sr2TbCu3O7 to the applied magnetic field have been studied by ac susceptibility measurements. Bo th the in-phase component chi' and the out-of-phase component chi'' of ac susceptibility are found to be sensitive to the frequency but not to the strength of the driving field. At high temperatures chi' exhibi ts Curie-Weiss behavior, it departs from this behavior as the magnetic correlations between the To spirts develop: and a cusp which is typic al of antiferromagnetic ordering is clearly revealed at lower temperat ures. The correlated Tb spins respond ''better'' to a driving magnetic field which has a lower frequency. The relative maximum of the d chi' /dT versus T plot matches to the T-N determined using neutron diffract ion measurements. This relative maximum continues to occur at the same temperature as the frequency of the driving field is varied. It, howe ver, shifts to a lower temperature as a de external field is applied, indicating the antiferromagnetic coupling between the To spins are wea ken by the de field. Moreover, the thermal behavior of chi'' exhibits a well-defined peak around the transition temperature, and a de field of strength 5 kOe smears the peak. (C) 1996 American Institute of Phys ics.