Bilayer Permalloy films grown in orthogonal applied fields

Permalloy bilayers grown in orthogonal applied fields demonstrated unusual coupling phenomena in Kerr-effect observations. The films were grown by ultrahigh-vacuum ion-beam sputtering in an applied field of 28 Oe that established a well-defined anisotropy direction. Midway through the deposition, the substrates were rapidly turned 90 degrees in the applied field, including an orthogonal anisotropy direction in the second layer of the film. With layers of equal thickness, a simple model predicts the bilayer to be isotropic in the plane of the film, regardless of the strength or mechanism of any interlayer coupling. Instead, the initial layer acquired the anisotropy orientation of the second layer grown. This unusual coupling was investigated for a number of bilayer structures of different thicknesses.<
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