Interaction of stress and magnetic properties in patterned copper-nickel-copper thin films

Abstract

In recent years, the epitaxial Cu/Ni/Cu thin film system has been extensively studied, due to its wide range of perpendicular magnetization. It has proved to be a model system to explore the interactions of strain, surface energies and magnetic properties. For that reason, is also an ideal system to explore the effects of patterning. It is expected that the miniaturization of patterned magnetic devices will be accompanied by a transition from polycrystalline to epitaxial films. This transition will require a detailed theoretical understanding of the interaction of strain and magnetic properties in patterned epitaxial magnetic thin films. The Cu/Ni/Cu film system is used in this work to explore a triaxial model for an orthorhombic symmetry of strain. By patterning the Cu/Ni into nanolines and measuring the resulting magnetic anisotropy, the validity of the model has been tested. It has been shown that upon patterning certain thicknesses of nickel into nanolines, the easy axis of magnetization shifts from out of the film plane to in-plane, transverse to the line direction, an observation at odds with the direction of magnetization predicted by shape considerations alone. This transition is explained by the dominant magnetoelastic energy for the Cu/Ni/Cu nanoline system.

(cont.) The resulting anisotropy values are consistent with strain relief values predicted by finite element modeling. In addition, the low temperature properties of the Cu/Ni/Cu epitaxial film system have been explored. The variation of the overall magnetic anisotropy as a function of temperature is found to be proportional to the cube of the reduced magnetization. In addition, the easy axis of magnetization for certain thicknesses of nickel has been found to shift from in-plane to perpendicular with the reduction of temperature.