Glassy Dynamics In Cumn Thin-Film Multilayers

Thin-film multilayered spin-glass CuMn/Cu structures display glassy dynamics. The freezing temperature T-f was measured for 40 layers of CuMn films of thickness L = 4.5,9.0, and 20.0 nm, sandwiched between nonmagnetic Cu layers of thickness approximate to 60 nm. The Kenning effect, T-f alpha lnL, is shown to follow from powerlaw dynamics where the correlation length grows from nucleation as xi (t, T) = c(1)a(0)(t/tau(0))(c2(T/Tg)), leading to [(T-f /T-g)c(2) ln(t(co)/tau(0))] + ln c(1) = ln(L/a(0)). Here, T-g is the bulk spin-glass temperature, c(1) and c(2) are constants determined from the spin-glass dynamics, t(co) is the time for the correlation length to growto the film thickness, tau(0) is a characteristic exchange time approximate to h/k(B)T(g), and a(0) is the average Mn-Mn separation. For t >= t(co), the magnetization dynamics are simple activated, with a single activation energy Delta(max)(L)/k(B)T(g) = (1/c(2))[ ln(L/a(0))-ln c(1)] that does not change with time. Values for all these parameters are found for the three values of L explored in these measurements. We find experimentally Delta(max)(L)/k(B) = 907, 1246, and 1650 K, respectively, for the three CuMn thin-film multilayer thicknesses, consistent with power-law dynamics. We perform a similar analysis based on the activated dynamics of the droplet model and find a much larger spread for Delta(max)(L) than found experimentally.