MAGNETORESISTANT CO/CU MULTILAYERS

In the last few years ferromagnetic / non-ferromagnetic multilayers have received considerable attention due to their great interest for magnetoresistive applications. Giant magnetoresistance has been observed in the Cu/Co system but with quite high saturation field (> > 1 kOe). In this paper we report on an original way to enhance this characteristic, using unusual fcc <100> cristallographic orientation. Special preparation of the <100> silicon substrates is investigated using in-situ kinetic ellipsometry, RHEED, grazing X-ray reflection and X-ray diffraction. We show that good quality fcc <100> pseudo-epitaxial copper surface can be obtained only when two condititions are fulfilled: first the silicon surface must be completely free of native oxide and second the copper buffer layer must be annealed under ultrahigh vacuum. Perfectly clean silicon surfaces are obtained by chemical etching followed by flash heating under ultrahigh vacuum. The copper buffer layer reacts with silicon and gives a textured fcc <100> Cu phase with a 45-degrees rotation of the Cu <100> lattice with regards to the Si <100> one. Additional annealing leads to an homogeneous interface silicide layer and improves the cristallinity of the Cu buffer layer. Cu/Co multilayers deposited on this kind of substrate show a well-defined fcc <100> texture for a large range of layer thickness. Oscillation of magnetoresistance with the copper thickness is observed with a period of about 10 angstrom . The maximum of magnetoresistance is found for 20.9 angstrom of cu (DELTAR/R congruent-to 6%), and the differential magnetoresistance is very high (DELTAR/RDELTAH = 1.4kOe-1). Combination of antiferromagnetic coupling and quadratic in-plane anisotropy of this special cristallographic orientation is responsible for this improvement.