Giant magnetoresistance in Co/Cu multilayers sputtered with Kr

The critical condition for the giant magnetoresistance (GMR) effect has not yet been fully clarified. Reports on the MR ratio of C o / C u multilayers (MLs) disagree as to whether the interfacial roughness or crystallinity of the MLs is the cause. The film morphology is significantly affected by sputtering conditions such as sputtering gas and pressure. This paper presents some results of the magnetoresistance, structure and morphology of C o / C u MLs sputtered with Kr gas. A comparison with Ar-gassputtered films is also presented. C o / C u MLs have been deposited by a conventional rf sputtering system in which one target position was used to fix two small targets of 4 cm diameter. The substrates, at ambient temperature, were positioned below the targets on a rotating table and the distance between target and substrate was 4 cm. Si(100) wafers were used as substrates. Background pressure prior to deposition was typically 1 x 10 -7 mbar. The sputtering gases were high-purity Kr and At. The number of bilayers ( N ) was typically 15 for all samples. Most of the films were deposited on a seedlayer of Fe. Firstly, the Ar pressure during sputtering was varied between 8.3 X 10 3 and 6.2 x 10 -2 mbar. It was confirmed that the Ar pressure was a crucial parameter in obtaining films with a good MR ratio. In the case of At, the maximum MR ratio was obtained at 3.1 × 10 2 mbar at a deposition rate of 1 , ~ / s for Co and 2 A / s for Cu. In Kr gas sputtering the gas pressure was kept constant at 2.2 × 10-2 mbar in order to achieve a deposition rate equal to that of Ar at 3.1 × 10 -2 mbar, because the deposition rate also affects the film morphology.