Controlling Anisotropy of NiFe Thin Films During Deposition for Device Applications

Thin film permalloy (with compositions around Ni80Fe20 continues to be an important ferromagnetic material for a range of applications including sensors, inductors and spintronic devices. Very weak magnetostriction and magnetocrystalline anisotropy are key attributes contributing to the favorable magnetic properties required in many such applications. Also in applications the anisotropy of the permalloy is controlled, usually by field-induced anisotropy or lithographic patterning. This work describes the control of anisotropy and the magnetization behavior in Permalloy thin-films by controlling the angle of the substrate with respect to the source during thin-film deposition. Film thicknesses from 5 nm up to 40 nm were investigated and all showed the development of a significant anisotropy and coercivity enhancement as the angle of the substrate was increased. Although this approach produces a well-defined in-plane easy axis, the orthogonal magnetization can be more complex than that of simple hard axis behavior. Deposition induced anisotropy effects were apparent even for a substrate tilt of only ten degrees. The control of anisotropy using this depositional effect was demonstrated for applications with examples showing control of magnetoresistance and via the competition between the deposition anisotropy and shape anisotropy in controlling the magnetization behavior of lithographically patterned structures.