Rare-earth spin-glasses with uniaxial anisotropy

The properties of spin-glasses with uniaxial anisotropy are investigated by magnetization measurements on single crystals of Y and Sc doped with Er, Dy, Tb, or Gd impurities. In alloys with strong anisotropy, spin-glass properties (susceptibility, cusp, irreversibility) appear only for fields along the c axis of the crystal (Ising-like systems) or only for fields in the basal plane (X-Y---like systems). The freezing temperature of the Ising-like systems is higher than that of the Heisenberg systems (alloys with Gd) by about a factor of 3. These results are in agreement with recent theoretical predictions. In alloys with small anisotropy, the irreversibility effects appear at the same temperature in longitudinal and transverse fields and we cannot identify the two-stage freezing predicted by the theory.