A perpendicularly exchange-coupled composite structure, which consists of a [Co/Ni]N multilayer and a ferrimagnetic TbCo layer, displays specific features when it is utilized as a reference layer in spin valves. By slightly increasing the TbCo thickness, the coercivity of the coupled structure greatly increases, thereby giving an effective way to widen the difference in switching fields for the free and reference layers, and making it possible to manipulate magnetizations parallel or antiparallel for a wide range of fields. Such composite reference layer cannot only maintain a high perpendicular giant magnetoresistive (GMR) ratio, but it also minimizes the field offset in the minor GMR curves due to the negligible stray field generated by the antiferromagnetically aligned moments in the reference layer.
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We would like to thank Professor Peter M. Levy for careful reading of this manuscript. This work is supported by the National Natural Science Foundation of China (Grant Nos. 50771032, 50771033, 11074046, and 61078030), the National Basic Research Program of China (Grant No. 2009CB929201), and the Innovation Program of Shanghai Municipal Education Commission (Grant No. 09ZZ03). B. Ma thanks for the support from the NSFC (Grant No. 51071046).