Magnetic anisotropy evolution with Fe content in electrodeposited Ni100−xFex thin films

Abstract

In this study, we have experimentally and theoretically determined how the magnetic anisotropy of Ni_100−xFe_x thin films evolves as a function of the Fe content in electrodeposited samples. When the Fe content is below 12 at%, stripe domains are promoted once the thickness exceeds a critical value. For an Fe content of 7 at%, the transcritical shape is present in the hysteresis loop for a thickness of 600 nm. However, for compositions equal to or above 12 at%, we have not found evidence of stripe domains, as indicated by the absence of the transcritical shape in the hysteresis loops for layer thicknesses as high as 1 μm even if a magnetic field is applied perpendicular to the sample plane during growth. All the studied layers are polycrystalline with a 〈111〉 texture. The experimental results are understood in the framework of a theoretical model which considers different contributions to the magnetic anisotropy: magnetocrystalline, magnetoelastic, magnetostatic and from pairs. Out-of-plane anisotropy promoted by columnar growth has not been considered as the saccharine-based electrolyte used for the electrodeposition prevents it. In fact, the magnetic anisotropy related to pairs, which is not generally taken into account in models for Ni_100−xFe_x, appears to play a crucial role in these thin films. Fitting of the experimental results to this model reveals that the local anisotropy generated by pairs can be as high as 3.30 × 10⁶ J m⁻³. This theoretical and experimental combined investigation highlights the relevance of all these fundamental mechanisms for the understanding and tuning of magnetic materials.