Influence of soft magnetic underlayers on the magnetic properties of Co90Fe10 films

• The coercive fields of CoFe films are reduced when grown on NiFe and Metglas layers.
• CoFe magnetostriction constants can be tuned by selecting the correct underlayer.
• Growing on NiFe is favourable to achieve soft CoFe films, than growing on Metglas.

The structure and magnetic properties of thin Co90Fe10 films have been studied to determine how different soft magnetic underlayers (Fe81B13.5Si3.5C2 (Metglas) and Ni81Fe19) influence these properties with the aim to achieve soft fcc Co90Fe10 films with large magnetostriction constants. The thickness of the Co90Fe10 films was 25 nm with the thickness of the magnetic underlayer ranging from 15 nm to 35 nm. The effect of applying a magnetic field during the growth of both layers was also investigated. From X-ray diffraction, it was found that the Co90Fe10 films grown on NiFe had lower in-plane stresses compared to those grown on silicon and Metglas. While the coercive fields of all the Co90Fe10 films were smaller than the monolith Co90Fe10 film, the magnetostriction constants were strongly dependent on the underlayer they were grown on. Thus it is possible to tune the magnetostriction constant of the Co90Fe10 film to be positive or negative by selecting the correct soft magnetic underlayer.