Misfit Accommodation in Thin Films of Nickel/copper as Measured by Magnetic Anisotropy.

The measurement of misfit strain and misfit accommodation in Ni/Cu (001) has been made in conjunction with measurements of magnetic anisotropy in order to explore the possibility of using anisotropy measurements as a convenient in situ method of strain evaluation in magnetic thin films. Epitaxial Ni films with thickness ranging between 10A and 200A were deposited using e-beam evaporation under UHV conditions on epitaxial Cu films grown on NaCl and Si substrates. Misfit dislocation content was characterized using transmission electron microscopy (TEM). Ni film strain was measured ex situ using substrate curvature measurements. Magnetic properties were determined qualitatively in situ using the magneto-optic Kerr effect. Magnetic anisotropy energy was measured ex situ using vibrating sample magnetometry. Microscopy results indicate the presence of two types of misfit dislocation at the Ni/Cu interface, 60^circ dislocations with Burgers vector inclined to the interface plane, and 90^circ dislocations with Burgers vector lying in the plane of the interface. Average dislocation spacing was measured using TEM, and was found to decrease with increasing Ni thickness. Strain measurements indicated that the increased misfit dislocation content resulted in a decrease in strain. In situ magnetic characterization showed that, for low Ni thicknesses (high strain), the preferred magnetization direction was perpendicular to the plane of the film. At higher thicknesses (lower strain) the preferred direction was in the plane of the film. Ex situ quantitative measurement of magnetic anisotropy energy confirmed this result. The anisotropy measurements, combined with strain measurements, were analyzed using a modified version of the Neel pair interaction model. From this analysis, values for the surface magnetocrystalline and surface magnetoelastic anisotropy energies were determined. A quantitative relationship between strain and magnetic anisotropy has therefore been established which is useful for in situ study of the strain and strain evolution in these films through magnetic characterization.