Nickel films deposited between amorphous silicon layers: Effects of annealing, Ni/Si interface and magnetic properties

Abstract

This study demonstrates exceptional magnetic properties associated with magnetic anisotropy in nickel layers approximately 23–28 nm thick, deposited between amorphous silicon layers (a-Si/Ni/a-Si) using triode sputtering. X-ray diffraction (XRD) analyses confirm the presence of the Ni phase in the samples. Furthermore, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) measurements reveal a trilayer structure consisting of nickel and silicon. These techniques also highlight the surface roughness of the nickel layer and detail the characteristics of the Ni/Si interface. Magnetic properties were evaluated using a vibrating sample magnetometer (VSM). The samples were annealed at temperatures up to 190 °C to optimize their magnetic characteristics. After annealing, the samples exhibited a high perpendicular remanence ratio (M_r/M_S ≈ 1), high perpendicular coercivity (H_C = 620 Oe), and a high effective perpendicular magnetic anisotropy energy density (K_eff*t ≈ 1.16 erg/cm²). These properties are particularly interesting because of the substantial thickness of the nickel layer. Achieving nickel films thicker than 15 nm with perpendicular magnetic anisotropy (PMA) has been challenging. The origin of PMA is attributed to magnetoelastic anisotropy and internal strains, which are related to diffusion processes and thermal expansion mismatch between the Ni layer and the Ni/Si and a-Si layers.