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 H-c, increased remanent squareness, and improved magnetic anisotropy due to the reduced roughness of the Nb underlayer, especially at high spatial frequency (>25 mu m(-1)). Typical results for 2.4 nm thick Ni80Fe20 films deposited on 100 nm thick Nb were an easy-axis coercivity H-ce = 3.7 Oe (compared to 6 Oe without underlayer smoothing), a hard-axis H-ch = 1.5 Oe (5.5 Oe without smoothing), an easy-axis remanent squareness (ratio of remanent and saturation magnetizations) Sq(e) = 0.92, a hard-axis remanent squareness Sq(h) = 0.25, and a uniaxial anisotropy H-k = 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.