Dependence of magnetic properties on micro- to nanostructure of CoNiFe films

The magnetic properties of electrodeposited CoNiFe films with thicknesses varying from 0.20 to 10 μm were studied. The films show a single face-centered-cubic CoNiFe phase with grain sizes ranging from 23 to 29 nm. The coercivity is controlled by a combination of the morphology and nanocrystalline structure of the deposits. The nanocrystalline grain size determines the intrinsic coercivity associated with crystalline anisotropy as in the random anisotropy model, whereas an additional morphology term of coercivity is controlled by the thickness inhomogeneity on a submicron scale. The thin films show considerable roughness and a higher coercivity, up to a level of 560 A m^-1 (7.0 Oe) in 250 nm films. The thick films show coercivity values of as low as 16 A m^-1 (0.2 Oe). The coercivity dependence on thickness was fitted using a simple model combining a morphology dependent additional contribution term to the random anisotropy model as H_c = H_c ^morph + H_c^anis. Good agreement between the model and the experimental results was obtained.