The development of magnetic materials on flexible substrates for spintronic applications

Abstract

Flexible electronic is a field of technology for assembling electronic circuits and devices on flexible substrates; which are characterized by their low cost, conformable and light weight properties compared to conventional silicon-based electronic devices. The addition of ferromagnetic materials to flexible substrates will allow the introduction of additional functionalities including memory and sensors. Here, I present a detailed study of the development of perpendicular magnetic anisotropy (PMA) in Pt/Co/Pt multi-layered systems and demonstrate the conditions for controlling the anisotropy. Two typical kinds of substrates have been introduced for preparing trilayer thin-film structure by deposition of magnetic films (Pt/Co/Pt) on them. Magnetron sputtering was used to deposit a series of Pt/Co/Pt trilayers where magnetic anisotropy was studied using Atomic Force Microscope, x-ray diffraction, x-ray reflectivity, Magneto-Optical Kerr effect magnetometry and Hall–effect measurements. The effect of Co thickness on the anisotropy, coercivity and switching behaviour were examined and compared between Hall–effect measurements and silicon substrates. The substrate was found to have a significant effect. A clear PMA was observed for Co thicknesses that range from 0.3 to 0.7 nm. Additional increments in the Co thickness makes the magnetization return to the in-plane direction, with a rapid drop in both the coercivity and the remanence. Further improvements in the PMA were obtained through the thickness of the Pt buffer layer, with higher coercive fields for both flexible plastic and silicon dioxide substrates. However, the thickness of the Pt capping layer did not have any systematic effect on the anisotropy. The results of a study of the interplay between microstructure and the magnetic properties of ultrathin Ru/Co/Ru and Pt/Co/Pt trilayer thin films with PMA is also presented. The maximum values of PMA are observed for the Co thickness by using Pt in comparison with Ru. The effective magnetic anisotropy and coercive field are very sensitive to Ru buffer layer thickness. The values of coercive field increase approximately from 10 of using Ru in comparison with about 1000 Oe for the Pt case. This is associated to the larger grains growth of Pt while Ru has a smaller grains growth. The surface roughness have an impact on the Hall resistivity on the ferromagnetic/non-magnetic thin films. Observation of the magnetic domain structure by means of polar kerr microscopy reveals that out-of-plane magnetization reversal occurs through then nucleation of bubbles on silicon dioxide.