Nonlinear susceptibility and relaxation in theXYspin glassYTb

Measurements of the nonlinear susceptibility, irreversibility onset, and relaxation of the remanent magnetization are reported for a single-crystal sample of YTb_30ex0exat.0ex0ex%. The data give strong support for the existence of a spin-glass phase transition for spin components in the basal plane, but not for those along the c axis. A scaling analysis of the nonlinear susceptibility leads to the values {δ}=3.2±{}0.2 and {φ}=3.0±{}0.2 for the field and cross-over exponents, respectively. These values are consistent with the position of the de Almeida--Thouless line observed below the freezing temperature.