Influence of substrate (Si and glass), Cu under-layer, in situ annealing of Ta/Cu and post-annealing on magnetic properties of [Co(0.3 nm)/Ni(0.6 nm)]4, 10 multilayer thin films

Abstract

Thin films of [Co(0.3 nm)/Ni(0.6 nm)]4, 10 multilayers (MLs) stack were deposited on Si and glass substrates using DC magnetron sputtering. The magnetic stack layers were deposited under various conditions such as (i) without using any under layer (referred as-prepared film) (ii) with Cu under-layer (iii) with in situ annealing of Ta/Cu under-layer (iv) with in situ along with post annealing of overall magnetic stack. The as prepared [Co(0.3 nm)/Ni(0.6 nm)]4 films deposited on Si as well as on glass substrate exhibit perpendicular magnetic anisotropy (PMA) as per magnetization measurements at room temperature. Inserting Cu under layer to this magnetic stack helps to enhance the coercivity (HC), saturation magnetization (MS) and the squareness [MR/MS] of the films in comparison to as-prepared MLs. Thin films of MLs with in-situ annealing of Ta/Cu, further enhance the value of MS and Sq in comparison to as-prepared and with Cu-under layer MLs. Even though the HC, MS and squareness [MR/MS] of M-H loop of post annealed films are comparable to the films prepared under other three conditions, the PMA was observed only in the latter case. Additionally, on increasing the number of magnetic bi-layers of the stack from 4 to 10 i.e. [Co (0.3 nm)/Ni (0.6 nm)]10, it is observed that the magnetic property parameters such as HC, MS and Sq were enhanced along-with exhibiting perpendicular magnetic anisotropy (PMA). The observation of PMA in these films may be due to the growth of Cu along (111) direction and Co/Ni (111) crystalline orientation, as demonstrated by XRD pattern and the topography analyses by AFM.