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 Ni 80 Fe 20 (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 ( $> 25\,\mu {\text{m}}^{- 1}$ ). Typical results for 2.4 nm thick Ni 80 Fe 20 films deposited on 100 nm thick Nb were an easy-axis coercivity $H_{{\rm{ce}}}= 3.7$  Oe (compared to 6 Oe without underlayer smoothing), a hard-axis $H_{{\rm{ch}}}= 1.5$  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.