Portal de Periódicos da CAPES

Glassy dynamics in CuMn thin-film multilayers

2017; American Physical Society; Volume: 95; Issue: 5 Linguagem: Inglês

10.1103/physrevb.95.054304

2469-9977

Qiang Zhai, David C. Harrison, Daniel Tennant, E. Dan Dahlberg, G. G. Kenning, R. Orbach,

Liquid Crystal Research Advancements

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 $\mathcal{L}=4.5,9.0$, and 20.0 nm, sandwiched between nonmagnetic Cu layers of thickness $\ensuremath{\approx}60$ nm. The Kenning effect, ${T}_{f}\ensuremath{\propto}ln\mathcal{L}$, is shown to follow from power-law dynamics where the correlation length grows from nucleation as $\ensuremath{\xi}(t,T)={c}_{1}{a}_{0}{(t/{\ensuremath{\tau}}_{0})}^{{c}_{2}(T/{T}_{g})}$, leading to $[({T}_{f}/{T}_{g}){c}_{2}ln({t}_{\text{co}}/{\ensuremath{\tau}}_{0})]+ln{c}_{1}=ln(\mathcal{L}/{a}_{0})$. Here, ${T}_{g}$ is the bulk spin-glass temperature, ${c}_{1}$ and ${c}_{2}$ are constants determined from the spin-glass dynamics, ${t}_{\text{co}}$ is the time for the correlation length to grow to the film thickness, ${\ensuremath{\tau}}_{0}$ is a characteristic exchange time $\ensuremath{\approx}\ensuremath{\hbar}/{k}_{B}{T}_{g}$, and ${a}_{0}$ is the average Mn-Mn separation. For $t\ensuremath{\ge}{t}_{\text{co}}$, the magnetization dynamics are simple activated, with a single activation energy ${\mathrm{\ensuremath{\Delta}}}_{\text{max}}(\mathcal{L})/{k}_{B}{T}_{g}=(1/{c}_{2})[ln(\mathcal{L}/{a}_{0})\ensuremath{-}ln{c}_{1}]$ that does not change with time. Values for all these parameters are found for the three values of $\mathcal{L}$ explored in these measurements. We find experimentally ${\mathrm{\ensuremath{\Delta}}}_{\text{max}}(\mathcal{L})/{k}_{B}=907$, 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 ${\mathrm{\ensuremath{\Delta}}}_{\text{max}}(\mathcal{L})$ than found experimentally.