Giant magnetoresistance studies in evaporated Ni–Fe/Cu and Ni–Fe–Co/Cu multilayers (abstract)

Abstract

Room temperature giant magnetoresistance (GMR) and magnetic properties of (Ni–Fe/Cu)n and (Ni–Fe–Co/Cu)n multilayers were investigated. Alternating layers of Ni–Fe–(Co) and Cu were electron-beam evaporated in a computer-controlled high-vacuum system at base pressure of ⩽4×10−8 Torr and deposition rates of ⩽2 Å/s. To complement and expand our previous investigation,1 GMR properties were additionally studied here as a function of cobalt content of Ni–Fe–Co films, the number (n) of bilayers, deposition temperature, and type of buffer layer. The Co content was varied from 7 to 17 at. %, and the number of bilayers ranged from n=8 to 20. No significant GMR was observed in the as-deposited multilayers. To produce tangible GMR, these multilayers were annealed between 300 and 360 °C for 2 h in a 150 Oe magnetic field in an argon atmosphere. The GMR effect (ΔR/R) was essentially independent of copper spacer thickness, which varied between 25 and 30 Å. For Co containing multilayers the highest ΔR/R=7.6% was obtained for 17 at. % Co deposited at 100 °C. The ΔR/R in all Ni–Fe–Co/Cu multilayers was sensitive to the deposition temperature, and R–H loops always showed significant hysteresis independent of the type of buffer layer. For application of these materials to very high density reproduce heads,2 the best results were obtained for (27 Å NiFe/25 Å Cu)14–18 multilayers deposited at 160 °C on 70 Å Ta buffer layer. For example, n=17 multilayers annealed at 350 °C exhibited ΔR/R=7.5%, half-width at half-maximum of ∼50 Oe, essentially no anisotropy, and virtually zero hysteresis (Fig. 1). Frequency dependent permeability measurements showed constant permeability between 10 and 200 MHz. Low- and high-angle x-ray diffraction as well as atomic force microscopy were used to investigate the effect of different geometries of multilayers on structure and roughness and to correlate them with GMR properties.