Role of low energy transition metal ions in interface formation in ZnO thin films and their effect on magnetic properties for spintronic applications

Abstract

In this study, X-ZnO/ZnO/Si(100) (X = Co, Ni and Cu) bilayer structure is fabricated using low energy ion implantation technique. Five different fluences 1 × 1015, 5 × 1015, 1 × 1016, 2.5 × 1016 and 5 × 1016 ions/cm2 with 100 keV ion-beam energy were selected in order to implant the ions up to the depth of ≈44 nm as calculated through Stopping Range of Ion in Matter and Transport Range of Ions in Matter software. Structural modification was investigated by high resolution X-ray diffraction measurements in ZnO bilayer system. An observed systematic 2θ shift in (002) peak with increasing fluence implies increased density of implanted metal ions in ZnO matrix revealing the substitution of implanted ion at Zn-site. The mechanism of bilayer formation by ion-beam implantation technique has been discussed for metal-ions by investigating their interface properties. Atomic force microscopy reveals the morphological modification after ion implantation. Near-edge X-ray absorption fine-structure (NEXAFS) measurements at metal K- and L3,2-edges have been used to investigate the nature of implanted ions in terms of their valance state and local electronic environment. Further, O K-edge NEXAFS measurement for Ni-ZnO/ZnO/Si bilayer is highly sensitive to incident beam angles whereas no spectral change is seen for Zn L-edge measurements. The magnetic measurements were performed via vibrating sample magnetometer that showed the films are ferromagnetic at room temperature. The origin of ferromagnetism has been understood through defect mediated bound magnetic polaron model. Further, perpendicular magnetic anisotropy is also observed for Ni-ZnO/ZnO/Si bilayer structure at room temperature, which is correlated with the angle dependent O K-edge NEXAFS measurements. Fabrication of ZnO bilayer via ion implantation and investigation of above properties may prove useful in spin related and optoelectronic applications.