Interface magnetism in Permalloy/Cu multilayers: Ferromagnetic-resonance study

Ferromagnetic resonance has been applied to study sputtered [Permalloy/Cu]₁₀₀ multilayers with Permalloy (Py) and Cu layers thicknesses 5 <dPy< 40 and 8 <dCu< 40, respectively. The effective magnetization is analyzed in the vicinity of nominal critical thicknesses of Py layers, 2Δd = 4.9, 7.6, and 8.3 {}, at 77, 293, and 400 K, respectively. From its behavior and the temperature measurements of ferromagnetic resonance (FMR) spectra we argue about the magnetic structure of a statistically averaged interface between Py and Cu: At room temperature, about 0.5 monolayer (ML) (1 ML = 1.8 {}) may be magnetically inactive due to spin wave excitations in ultrathin films and about 1.5--2 monolayers---due to intermixing resulting from roughness. Trapezoidal-like magnetization profiles in ultrathin Py layers 4--7 monolayers thick are discussed in terms of percolation of magnetic clusters within a rough interface. The FMR linewidth depends on the thickness of Py layer as dPy^-2.