Engineering coercivities by dual ion beam sputtering for synthesizing soft permalloy-based spin-valve multilayers (abstract)

Abstract

Thin permalloy (Ni80Fe20) single-layer films and multilayers were fabricated onto Ta-buffered oxidized silicon substrates using a prototype dual ion beam sputtering system (Commonwealth Scientific Corporation). The room temperature substrates were placed in a uniform in-plane magnetic field during growth (∼150 Oe) yielding a uniaxial magnetic anisotropy in the permalloy films (typically ∼6 Oe). An examination of single-layer permalloy films with thicknesses from 20–50 nm indicated that the presence of an ∼100 eV ion-beam assist beam focused directly onto the substrate during film growth consistently modified the coercive and remnant characteristics of the films. Typically, the nonion beam assist modified NiFe films exhibited a coercivity ∼1 Oe, while the ion beam assist modified films exhibit a slightly larger coercivity (∼1.5 Oe). Based on this apparent influence of the assist ion beam treatment on the film coercivity, the fabrication of soft spin-valve multilayer structures exploiting differences in the ion beam treatment of chemically identical ferromagnetic layers seemed plausible. To test this idea ,two parallel series of multilayers composed of [2.5 nm permalloy]-[Cu (2.5 nm, 4 nm, or 5.5 nm)] or [0.3 nm Co-1.9 nm permalloy -0.3 nm Co]-[Cu (2.5 nm, 4 nm, or 5.5 nm)] were fabricated. In these 30 cycle multilayers, alternating ferromagnetic layers were subjected to a 150 eV assist ion beam treatment during growth (higher coercivity layer), or to NO assist ion beam treatment during growth (lower coercivity layer). VSM analysis revealed that the simplest uncoupled spin-valve multilayer configuration consisted of the [2.5 nm permalloy]-[4 nm Cu] multilayer with Hc1 ∼0.8 Oe and Hc2 ∼2.2 Oe, and the [0.3 nm Co - 1.9 nm permalloy - 0.3 nm Co] - [4 nm Cu] multilayer with Hc1 ∼ 3 Oe and Hc2 ∼ 15 Oe. Film analysis by low-angle x-ray diffraction and reflectivity, as well as the effect of the Co interface layer on GMR properties will also be reported.