Comparison of magnetic coupling between permalloy films separated by Cr for polycrystalline and epitaxially grown structures

Two series of magnetic multilayers consisting of two 600 Å permalloy (Ni₈₃Fe₁₇) layers separated by varying thicknesses of Cr, sandwiched between two further layers of Cr have been studied by spin wave resonance (SWR). One series of samples has polycrystalline layers, and for comparison a second series of epitaxial layers were grown on GaAs(100) substrates. The (100) epitaxy of the silver buffer layer with the GaAs(100), is followed by the (100) epitaxy of the Cr layer. A four domain (011) epitaxy for the permalloy is deduced from the symmetry of the Cr and permalloy layers. For the polycrystalline layers the magnetic coupling is observed to decrease monotonically to zero. The epitaxial layers show evidence of oscillatory exchange coupling; this is discussed with respect to its long period and interfacial roughness