Magnetoresistance of CO / Cu / CO Spin Valve Sandwiches

The dependence of magnetoresistance (MR) ratio on various variables like the thickness of the second Co layer, on the presence of cap layer, on deposition field (Hdep) and on annealing in Co/Cu/Co sandwiches was investigated. Spin-valve sandwiches were deposited on the corning glass by means of the 3-gun dc magnetron sputtering at a 5 mTorr partial Ar pressure and room temperature. The deposition field was varied from 70 Oe to 720 Oe. The MR curve was measured by the four-terminal method with applied magnetic field up to 1000 Oe perpendicular to the direction of a current in the film plane. The MR ratio of glass/Fe(50Å)/Co(17Å)/Cu(24Å)/Co(tÅ) fabricated by making 50 Å of Fe buffer layer has the maximum value of 8.2% when the thickness of the second Co layer was 17 Å and the deposition field was 350 Oe. In the case of glass/Fe(50Å)/Co(17Å)/Cu(24Å)/Co(tÅ) with Cu cap layer on top, the decrease in the MR ratio seemed to relate with the oxidation of the second Co layer. Samples prepared with deposition field showed greater MR ratios through the formation of more complete spin valve films. After annealing for 2 hours at 300℃, the MR ratio of the samples prepared with deposition field decreased rapidly while the MR ratio of the sample prepared without the field remained.