Investigation of soft magnetic properties of Ni/Cu multilayer films: Definitive screening design and response surface methodology

Abstract

Ni/Cu multilayer films have been found to be highly promising due to their applications in magnetoresistive sensors. Therefore, this study aims to find the optimum conditions for the production of Ni/Cu films with soft magnetic properties of by monitoring the maximum saturation magnetisation, M-s, and minimum coercivity, H-c. Thus, a relatively new class of experimental design called "definitive screening design (DSD)" was adopted for this investigation. Subsequently, response surface methodology (RSM) was applied to obtain an optimum deposition recipe for soft magnetic Ni/Cu multilayer films. A 13-run experiment from DSD approach was employed on the deposition of the multilayer films. Magnetic properties of the films were measured by a vibrating sample magnetometer. The influence of simultaneously varying factors of total thickness (TT), Ni deposition rate (Ndr), Cu deposition rate (Cdr), Ni layer thickness (Nlt) and rotation of the substrate (RS) on maximum M-s and minimum H-c responses was investigated. The most effective and interactive factor that was obtained from mean response characteristics and counter plots for both M-s and H-c values is Nlt. The optimum experimental conditions were obtained as TT (100 nm), Ndr (0.02 nm/s), Cdr (0.1 nm/s), Nlt (8.8 nm) and RS (20 rpm). After experimental analysis of optimisation process, the M-s of the films increased from 472.5 to 537.2 emu/cm(3), while the H-c decreased from 37 to 28 Oe. Structural analysis of the films was carried out by X-ray diffraction. All films showed face-centred cubic (fcc) structure and the preferential orientations were (111) for the films. The quadratic regression was successfully applied and shown to estimate the M-s (522.6 emu/cm(3)) and H-c (31 Oe) values by using optimal conditions. It is observed that the experimental results and predicted values were very close to each other. The results demonstrated that optimal values for the production factors can be efficiently used to obtain maximum M-s and minimum H-c of the films synthesis process.