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

巨磁电阻(简称GMR或MR)材料是通过溅射或离子镀等蒸发方法制备的，也发展了用于制备MR材料的电镀或机械合金化方法。为了能够容易地制备大尺寸MR材料，本文采用一种新的叠轧和热处理相结合的方法在铜上电镀钴，研究了各种显示巨磁电阻效应的叠层材料。在厚度为9微米和16微米的薄铜箔的两侧电镀厚度为1.7~50微米的钴，然后在流动的氢气气氛中(压力：66.7帕)将它们与相同尺寸的铜箔在1173K下焊接14.4K，然后分别堆叠24~400层镀钴铜箔和切割到10×45 mm^2的纯铜。连接的样品厚度约为这样制备的样品在Tempe…室中重复滚动在轧制过程中，在不进行热处理的情况下，将厚度提高到16微米左右。此外，将轧制的材料切割成10×45 mm^2的尺寸，堆叠、连接和轧制。最后，得到厚度为10到60微米的2000层到4100万层的样品。这些样品在流动的氢气气氛中(压力：66.7Pa)在573~873K的温度范围内进行3.6K的热处理，然后冷却到室温。用扫描电子显微镜观察了这些样品的微观结构，并在室温和77K下测量了所有样品的MR。本文研究的铜-钴二元系在室温下的MR最大值约为24%。如此大的MR值将导致分散在铜相中的Co粒子间距变小。随后进行了向室温淬火的操作在1173K下连接形成了铜相与溶解钴的过饱和固溶体。在室温下反复轧制也使过饱和固溶体强制形成过饱和固溶体。热处理使过饱和的钴以细小的弥散颗粒析出在铜相基质中。对1.7×m厚的电镀钴层和16×m厚的钴箔交替堆叠到399层的样品的能谱分析分别显示出12at%和15at%的Co。这些样品的横截面上的结构是片状的。12at%的Co-Cu的磁阻比随还原比的变化而敏感地变化，虽然受热处理时间的影响较小，但15at%Co-Cu合金的磁流变率比12at%Co-Cu钢的高，合适的层压次数和热处理比层压次数会产生较大的磁流变率，只有增加层压次数才能抑制细化Co颗粒的尺寸。较少

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