Improvement in the magnetic properties of Ni-Fe thin films on thick Nb electrodes using oxidation and low-energy ar ion milling

We developed a method to engineer the surface topography of Nb underlayers using surface oxidation followed by low-energy Ar ion milling to improve the properties of subsequently deposited magnetic Ni80Fe20 (Permalloy) thin films. They had reduced coercivity Hc, increased remanent squareness, and improved magnetic anisotropy due to the reduced roughness of the Nb underlayer, especially at high spatial frequency (>25 μm^-1). Typical results for 2.4 nm thick Ni₈₀Fe₂₀ films deposited on 100 nm thick Nb were an easy-axis coercivity Hce = 3.7 Oe (compared to 6 Oe without underlayer smoothing), a hard-axis Hch = 1.5 Oe (5.5 Oe without smoothing), an easy-axis remanent squareness (ratio of remanent and saturation magnetizations) Sqe = 0.92, a hard-axis remanent squareness Sqh = 0.25, and a uniaxial anisotropy Hk = 6.0 Oe, all measured at a temperature of 10 K. This ion-smoothing technique could potentially be used to improve the properties of magnetic layers in superconducting memory and other magnetoelectronic devices that utilize a thick underlayer that serves as an electrical contact.