Effect of Ta Underlayer on Thickness-Dependent Magnetic Properties of Ni–Fe Films

Abstract

We report the effect of Ta underlayer on the structural and the magnetic properties of Permalloy (Ni81Fe19) thin films over a wide range of film thicknesses ( t Ni–Fe = 10–200 nm). For this purpose, Ta (5 nm)/Ni–Fe ( t Ni–Fe nm)/Ta (2 nm) films were grown on thermally oxidized Si substrates under the presence and the absence of biasing magnetic field (1000 Oe). The Ni–Fe films grown under the presence and the absence of biasing magnetic fields are referred to Ta/Ni–Fe(M) and Ta/Ni–Fe(NM), respectively. X-ray diffraction studies revealed that the Ta underlayer plays an important role in the formation of fcc-(111) Ni–Fe texture in both the Ta/Ni–Fe(M) and Ta/Ni–Fe(NM) films. In addition, the values of average crystallite size depend on the film thickness, biasing field, and Ta underlayer. Thickness-dependent magnetic hysteresis ( M–H ) loops demonstrate a strong in-plane uniaxial anisotropy in both the Ta/Ni–Fe(NM) and Ta/Ni–Fe(M) films. The uniaxial anisotropy constant ( Ku ) depends not only on the film thickness, but also strongly on the biasing magnetic field. Coercivity decreases with increasing film thickness for both the Ta/Ni–Fe(NM) and Ta/Ni–Fe(M) films, and approaches to a minimum of $\sim$ 0.4 Oe even at t Ni–Fe = 200 nm. Furthermore, the observed magnetic domain patterns of Ni–Fe films show their dependence on the Ta underlayer, biasing field, and Ni–Fe thickness. The effects of the Ta underlayer, the Ni–Fe film thickness, and the biasing-field driven uniaxial anisotropy on the structural and the magnetic properties are discussed on the basis of reduction in strain at the Ta/Ni–Fe interface.