Development of super-laminated magneto-resistance materials of copper-cobalt using by electroplating and repeated rolling

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Giant magneto-resistant (abbreviated as GMR or MR) materials are prepared by such evaporation methods as sputtering or ion plating techniques.Electroplating or mechanical alloying method for preparing MR materials is also developed.In order to be able to easily prepare large size MR materials, various laminated materials that reveal GMR has been investigated in the present study by a new combination system of repeated rolling and heat treatment followed electroplating cobalt on copper.Cobalt was electroplated in the thickness from 1.7 to 50 mum on both sides of thin copper foil of 9 or 16 mum in thickness.Then they were joined with same size copper foil at 1173 K for 14.4 ks in a flowing hydrogen gas atmosphere (pressure : 66.7 Pa) followed stacking 24 to 400 layers alternatively copper foil coated with cobalt and pure copper cut to 10X45 mm^2 respectively.Joined samples were in the range of thickness from about 220 to 4500 mum.Such prepared samples were repeatedly rolled at room tempe … More rature to about 16 mum in thickness without annealing during rolling.Moreover, rolled material was cut to size of 10X45 mm^2, stacked, joined, and rolled.Finally, samples were gotten from 2000 layers to 41,000,000 layers in the thickness of 10 to 60 mum. These samples were heat-treated in the range of temperature from 573 to 873 K for 3.6 ks in the flowing hydrogen gas atmosphere (pressure : 66.7 Pa) and cooled to room temperature.Microstructure of these samples were observed using a scanning electron microscope and MR of all samples were measured at room temperature or at 77 K.The maximum MR of Cu-Co binary system in the present study shows about 24% at room temperature.Such big value of MR would be caused to small inter-spacing of dispersed Co particles in the matrix of Cu phase.The operation of quenching to room temperature followed joining at 1173 K formed supersaturated solid solution of Cu phase with dissolved cobalt.Moreover, repeated rolling at room temperature also made forcedly the supersaturated solid solution.The supersaturated cobalt was precipitated as fine dispersed particles in the Cu phase matrix by heat-treatment.Energy dispersed spectroscopy analysis on a cross section of a sample which 1.7 *m thickness of electroplated Co layer and 16 *m thickness Co foil were alternatively stacked to 399 layers showed l2at%Co and l5at%Co, respectively.The structure on the cross section of these samples was observed as lamella.MR ratio of 12at%Co-Cu was sensitively changed by reduction ratio, though it was slightly effected by heat treatment time.Almost 15at%Co-Cu showed higher MR ratio than that of 12at%Co-Cu.Large MR ratio would be revealed by a suitable laminated number and heat treatment rather than by laminated number.Only increasing laminated number would suppress refining Co particle size. Less