Electron-spin-resonance linewidth of multilayered CuMn/Cu spin glasses: Residual width and thermal-broadening coefficient

The electron-spin-resonance (ESR) linewidth {Δ}H(T) has been measured in multilayered Cu_1-x{Mn}ₓ$/Cu (x=0.07,0.11) as a function of spin-glass layer thickness ${W}SG(1 nm≤{W}SG≤1000 nm). For temperatures well above the freezing temperature{T}f, ΔH(T)=A+BT, where A is the residual linewidth and B the thermal-broadening coefficient. The residual linewidth increases with decreasing{W}SG$, indicating that the paramagnetic Curie-Weiss temperature FTHETA and/or the inhomogeneous broadening depend on ${W}SG. Preliminary high-temperature-susceptibility measurements confirm that θ decreases with decreasing{W}SG$, but are not sensitive enough to determine quantitatively if this change is entirely responsible for the observed changes in A. The thermal-broadening coefficient B characterizes the strength of the ESR bottleneck. As WSG decreases, B increases, indicating the breaking of the bottleneck via the presence of additional relaxation paths. Possible mechanisms for these paths are suggested. The increase in B with decreasing WSG is similar to that observed with increasing concentration of a third element in bulk spin glasses. Possible links between decreasing WSG and increasing anisotropy are considered. Data parametrized in terms of {ε}, where {ε}=[Tf({∞})-Tf(WSG)]/Tf({∞}), show that both A and B increase linearly with increasing {ε} over the entire range of {ε} studied.