Magnetoresistance in Co/Cu Multilayers

Co/Cu multilayer films were prepared by rf sputtering, both with and with-out a substrate bias voltage VB=¿30 V. X-ray diffraction results indicated that the layer boundaries in ¿30 V biased films are sharper, and the orientation of (111) planes are better, than in films prepared without a bias voltage. In films with zero bias, the MR ratio increases monotonically with the Cu layer thickness dCu up to about 40 Ã…, and then decreases. On the other hand, in films prepared with a ¿30 V bias the MR ratio oscillates with dCu, and peaks appeared at dCu= 23, 36 and 48Ã…. The maximum MR ratio was obtained for the structure [Co(15.1 Ã…)/Cu(24.3 Ã…)]30/Cu(50 Ã…), with a value of 13.1% at room temperature and 17.0% at 110K. In this film, the interlayer coupling strength J was very small, 0.008 erg/cm². The sharpness of the MR change, ¿R/R(Hs)·¿H, was a very large 2.2 kOe^¿1 The different dCu dependences of films prepared with a ¿30 V bias and with zero bias is thought to originate in the different qualities of the layer boundaries. The extraordinary Hall effect and the planar Hall effect are discussed.