Magnetoimpedance effect of FINEMET ribbons coated with Fe₂₀Ni₈₀ permalloy film

To study the electromagnetic interaction mechanism between different soft magnetic materials, a series of specimen with different thickness Ni₈₀Fe₂₀ film were deposited onto nanocrystalline Fe_73.5Cu₁Nb₃Si_13.5B₉ ribbons by magnetron sputtering. X-ray diffraction revealed a slightly structural variation of the ribbons as thickness of the Ni₈₀Fe₂₀ film ranging from 0 to 520 nm. The surface roughness of Ni₈₀Fe₂₀ layer was investigated by Atomic Force Microscopy, showing no significant variation with different thickness of Ni₈₀Fe₂₀ layer. The hysteresis loops and the coercivity value indicated the shift of anisotropy direction from parallel to normal to the surface as the Ni₈₀Fe₂₀ thickness increased, thus influencing the magnetic exchange interaction. Compared to the bare Fe_73.5Cu₁Nb₃Si_13.5B₉ ribbons, coating of Ni₈₀Fe₂₀ films significantly enhanced the giant magnetoimpedance response of the ribbons. The 24% improved GMI ratio was achieved in the ribbon with 260 nm thick Ni₈₀Fe₂₀ film.