The structure, magnetic properties, optical properties and adhesion efficiency of CoFeBY films were studied. Co₄₀Fe₄₀B₁₀Y₁₀ alloy was sputtered onto Si (100) with a thickness of 10–50 nm, and then annealed at room temperature, 100 °C, 200 °C and 300 °C for 1 h. X-ray diffraction (XRD) showed that the CoFeBY films deposited at room temperature are amorphous. Annealing at 100 °C gave the films enough thermal energy to change the structure from amorphous to crystalline. After annealing, the CoFeBY thin film showed a body-centered cubic (BCC) CoFeB (110) characteristic peak at 44°. However, the low-frequency alternative-current magnetic susceptibility (χ_ac) and saturation magnetization (M_S) increased with the increase of thickness. CoFeBY thin films had the highest χ_ac and M_S after annealing at 300 °C compared to that at other temperatures. After annealing at 300 °C, the surface energy of CoFeBY film is the maximum at 50 nm. Higher surface energy indicated stronger adhesion.

When B and V are added to CoFe material, the mechanical strength and spin tunneling polarization of a CoFe alloy can be improved and enhanced by the high tunneling magnetoresistance (TMR) ratio. Based on these reasons, it is worthwhile investigating Co₄₀Fe₄₀V₁₀B₁₀ films. In this work, X-ray diffraction (XRD) showed that Co₄₀Fe₄₀V₁₀B₁₀ thin films have some distinct phases including CoFe (110), CoFe (200), FeB (130), and V (110) diffracted peaks with the strongest diffracted peak for 30 nm. The lowest low-frequency alternate-current magnetic susceptibility (χ_ac) was detected at 30 nm because the large grain distribution inducing that high coercivity (H_c) enhances the spin coupling strength and low χ_ac. The external field (H_ext) had difficulty rotating in the spin state, hence, the spin sensitivity was reduced and the χ_ac value decreased due to increased surface roughness. The 20 mm thickness had the highest χ_ac 1.96 × 10⁻² value at 50 Hz of an optimal resonance frequency (f_res). The surface energy increased from 34.2 mJ/mm² to 51.5 mJ/mm² for Co₄₀Fe₄₀V₁₀B₁₀ films. High surface energy had corresponding strong adhesive performance. According to the magnetic and surface energy results, the optimal thickness is 20 nm due as it had the highest χ_ac and strong adhesion.

In this study, the addition of Y to CoFeB alloy can refine the grain size to study the magnetic, adhesion and optical properties of as-deposited and annealed CoFeB alloy. XRD analysis shows that CoFeB(110) has a BCC CoFeB (110) nanocrystalline structure with a thickness of 10–50 nm under four heat-treatment conditions, and a CoFeB(110) peak at 44° (2θ). The measurements of saturation magnetization (M_S) and low frequency alternate-current magnetic susceptibility (χ_ac) revealed a thickness effect owed to exchange coupling. The maximum M_S of the 300 °C annealed CoFeBY film with a thickness of 50 nm was 925 emu/cm³ (9.25 × 10⁵ A/m). The maximum χ_ac value of the 300 °C annealed CoFeBY nanofilms with a thickness of 50 nm was 0.165 at 50 Hz. After annealing at 300 °C, CoFeBY nanofilms exhibited the highest surface energy of 31.07 mJ/mm², where the thickness of the nanofilms was 40 nm. Compared with the as-deposited CoFeBY nanofilms, due to the smaller average grain size after annealing, the transmittance of the annealed nanofilms increased. Importantly, when a CoFeB seed or buffer layer was replaced by a CoFeBY nanofilm, the thermal stability of the CoFeBY nanofilms was improved, promoting themselves on the practical MTJ applications.