Finite-size effects in the spin glass (SG) Cu-Mn have been studied using magnetron-sputtered multilayer systems (MSs) of the form Cu1-xMnx/Cu and Cu1-xMnx/Si with x=0.04, 0.07, 0.14 (and some data for 0.21). The SG layers have widths WCu-Mn ranging from 10 000 to 20 and are separated and magnetically decoupled from each other by interlayers of either 300 of Cu or 70 of Si. The MSs continue to show SG peaks in the zero-field-cooled (ZFC) dc magnetic susceptibility down to WCu-Mn=20. The quasistatic freezing temperature Tf (defined as the location of the peak in) begins to decrease from its bulk value, Tfb, at WCu-Mn 1000 and approaches zero for SG thicknesses 0 WCu-Mn 10 with Cu interlayers or 30 WCu-Mn 35 with Si interlayers. A plot of the ratio Tf/Tfb versus WCu-Mn yields a separate universal curve for each of the two interlayer materials, independent of x. Structural analyses of the MSs using large- and small-angle x-ray diffraction, energy-dispersive x-ray spectroscopy, selected area diffraction, electron microscopic imaging, and parallel resistivity measurements, confirm that the samples are layered and indicate that interface intermixing is modest in the Cu1-xMnx/Cu MS but more substantial in the Cu1-xMnx/Si MS. This latter result suggests that the Cu1-xMnx/Cu MSs are closer to isolated, uncontaminated layers of Cu-Mn, and further analysis thus focuses primarily upon these MSs. Various effects that might mimic size-dependent behavior are first considered, and then the universal variation of Tf/Tfb with WCu-Mn for the Cu1-xMnx/Cu MS is analyzed in terms of (1) static finite-size scaling and (2) the activated dynamics of the Fisher and Huse cluster-excitation model. Appropriate parameters are derived for each model. This investigation is believed to be the first to examine how the properties of a long-range Ruderman-Kittel-Kasuya-Yosida SG such as Cu-Mn change as the lower critical dimension is crossed. © 1990 The American Physical Society.
