CRITICAL-BEHAVIOR OF TRANSVERSE AND LONGITUDINAL AC SUSCEPTIBILITIES IN A RANDOM ANISOTROPY MAGNET A-DY16FE84

We have investigated critical lines in the H-T plane in a random aniso tropy magnet (RAM) a-Dy16Fe84 with a small effective ratio of the anis otropy (D) to the exchange constant (J) by means of ac susceptibility (chi) in static fields H parallel and perpendicular to the ac field. W e found that the transverse chi exhibits an anomaly along the irrevers ible line H(T(f)) determined by previous magnetization measurements, w hile the longitudinal X does so along a characteristic line H(T(i)) in a lower temperature region. Above H(T(f)) we also found an extra char acteristic line H(T(c)). The lines were almost independent of the meas ured frequency. Both the present results and previous magnetization re sults suggest that an equilibrium phase transition occurs, and the cri tical lines analogous to those in Heisenberg spin glasses are present in a weak RAM.