Etude des propriétés physiques des couches minces de Ni et des bicouches Ni/Cu préparées par évaporation sous vide

Abstract

Series of Ni thin films have been deposited by thermal evaporation onto glass, Si, mica, Al2O3, Cu and CuZn substrates with and without a Cu underlayer. The Ni thicknesses, t, are in the 4 to 163 nm range. The Cu underlayer has also been evaporated with a Cu thickness equal to 27, 52 and 90 nm. The effects of substrate, the Ni thickness and the Cu underlayer on the structural, electrical and magnetic properties of Ni are investigated. Rutherford Backscattering Spectroscopy was used to probe the Ni/Substrate and Ni-Cu underlayer interfaces and to measure both Ni and Cu thicknesses. The texture, the strain and the grain size values were derived from X ray diffraction experiments. The surface morphology is studied by means of a Scanning Electron Microscope. The electrical resistivity is measured by the four point probe. Magnetic properties were studied bay Vibrating Sample Magnetometer (VSM) and magneto-optic Kerr effect technique. The Ni films grow with the texture on all substrates. The Ni grain sizes D increase with increasing thickness for the glass, Si and mica substrates and decrease for the Cu one. The strain ε is positive for low thickness, decreases in magnitude and becomes negative as t increases. With the Cu underlayer, the growth mode goes through two phases: first, the stress (grain size) increases (decreases) up to a critical thickness tCr, then stress is relieved and grain size increases. For VSM, the hysteresis curves show an in-plane magnetic anisotropy for all samples. The first system (Ni/substrates) shows the coercivity increases with increasing thickness. The saturation field and squareness range from 0.22 KOe to 2.4 KOe and from 0.23 to 0.90, respectively. For the Ni/Cu/substrates system, the coercivity varies from 3 à 230 Oe. The squarness ranges from 0.08 to 0.67 and the saturation field varies from 0.52 KOe to 3.2 KOe. Kerr effect in the first system shows the coercivity and saturation field increase with increasing thickness and grain size. The squareness ranges from 0.45 to 0.91. For the second system, the coercive field varies from ~ 2 to 151 Oe when increasing thickness. The squarness ranges from 0.1 to 0.85 and the saturation field varies from 25 to 320 Oe.