Structural and magnetic properties os Si(100)/Ta/Co multilayers for spintronics applications

Abstract

This thesis is concerned with the structural and magnetic properties of Si(100)/Ta/Co single and multilayer thin films grown by DC magnetron sputtering technique. The structural properties of the films have been studied by X-Ray Diffractometer (XRD), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). This study revealed that a single Co film grows amorphous on silicon substrate up to 50 nm at room temperature. After this thickness, Co starts crystallizing in hexagonal (002) plane. The same crystallinity was also observed for 25 nm amorphous Co which was annealed at 4500C at high vacuum for 30 minutes. The presence of a single crystalline tetragonal Ta phase (-Ta) with the orientation along (002) has been observed for 40 nm Ta growth on silicon substrate. The Si(100)/Ta/Co bilayers and multilayers show good crystallinity for both Ta and Co films. SEM and AFM results show that all the single and multilayers grew uniform, continuous and with very low surface roughness. The magnetic properties of the films were investigated using Vibrating Sample Magnetometer (VSM), by measuring hysteresis loops. The effects of the thickness and growth pressure on the magnetic properties of Co films were studied. The easy magnetization axis of the samples is found to be parallel to the Co film plane. As the Co film thickness increased from 4 nm to 15 nm, the coercivity (Hc) decreased from 72 G to 20 G and after a threshold thickness it increased almost linearly up to 180 G for 100 nm film while the magnetization decreased. Moreover, it has been observed that as the Co growth pressure increases, the Hc value of Co films increases. Finally, we obtained two different Hc values for our MTJ sandwich with the structure of Si(100)/Ta/Co/TaOx/Co/Ta.