CRITICAL-BEHAVIOR OF THE ELECTRON-SPIN-RESONANCE LINEWIDTH IN MULTILAYERED CU0.89MN0.11/CU SPIN-GLASSES

The temperature dependence of the electron-spin-resonance linewidth, DELTAH(T), has been measured in multilayered Cu0.89Mn0.11/Cu as a function of spin-glass layer thickness W(SG) with 1 nm less-than-or-equal-to W(SG) less-than-or-equal-to 500 nm. We find that the critical behavior, as characterized by the divergence strength C and exponent kappa changes systematically with W(SG). A function parametrized in terms of the ratio of the freezing temperature in a sample with spin-glass layer thickness W(SG) to that of the bulk, T(f)(W(SG))/T(f)(infinity), describes all data with W(SG) greater-than-or-equal-to 7 nm. Samples with W(SG) less-than-or-equal-to 3 nm do not obey this form and are better described by a two-dimensional form that diverges as T-2.5. A universal function describing a crossover from three-dimensional to two-dimensional behavior as the layer thickness changes is suggested. Once the dependence of the critical part of DELTAH(T) on T(f)(W(SG)) is known, finite-size and droplet relationships can be used to infer the dependence on W(SG). The possibility that this crossover is due to increasing anisotropy as W(SG) is decreased is briefly discussed.