Correlation of magnetotransport and structure in sputtered Co/Cu multilayers

Abstract

Magnetic multilayer structures of Co/Cu prepared by dc magnetron sputtering are studied with respect to changing number of bilayers (N) for different thicknesses of the Cu spacer layer corresponding to different coupling conditions according to the oscillatory interlayer exchange coupling. X-ray reflectivity and diffuse scattering show that the multilayers become smoother with increasing N. The growth exponent of the roughness is found to be lower for a multilayer than for a single-layer film of similar thickness. The roughness of subsequent interfaces along the stack is conformal, and the lateral correlation does not change with the period number, but depends on the thickness of the spacer layers. The improved layer structure for larger N increases the antiferromagnetic coupling fraction as inferred from magneto-optic Kerr effect measurements and thereby increases the giant magnetoresistance (GMR) ratio up to 35% for N = 10. Thus, the first few bilayers do not contribute to the GMR but act as a buffer to improve the growth conditions for the following bilayers. The first about five bilayers can be replaced by a bottom Co layer of equivalent thickness which also improves the layer structure for a subsequently deposited lower number of bilayers without much loss in the GMR ratio. This smoothening effect due to the increasing of the thickness of the bottom-most layer is related to the simultaneously decreasing grain size.

Spin polarization and exchange coupling of Cu and Mn atoms in paramagnetic CuMn diluted alloys induced by a Co layer

“…The rms topological roughness values are approximately 5 Å for all CuMn/Co, Co/CuMn, Cu/Co, Co/Cu, CuMn/Cu, and Cu/ CuMn interfaces. The amplitude of the in-plane correlation length and the topological roughness are in agreement with previous observations in Co/Cu multilayers grown by magnetron sputtering 31,32 while the jaggedness of the interfaces shows no significant difference.…”

Field-dependent magnetic domain structure in antiferromagnetically coupled multilayers by polarized neutron scattering

“…We also like to mention, that our fits yield a structural interface rms roughness Ϸ 0.6 nm, which is in good agreement with the values from our previous x-ray reflectivity measurements. 7 The presence of this broad AF-coupled Co layers. As SF intensities arise from the magnetization components perpendicular to H a , we find that some columnar domains maintain the AF-coupled state and their magnetizations remain along the easy axis ͑i.e., perpendicular to H a ͒.…”

“…These MLs show a high degree of morphological vertical correlation and small lateral correlation of the interface roughness. 7 We observe the domain structure of the Co layers to evolve from large to small vertically correlated domains along the stack. The larger ones remain AF aligned beyond the apparent saturation field, while the antiparallel alignment for the smaller breaks up at lower external fields.…”

“…In previous work, we have observed that the strength of the AF coupling and the GMR values correlate with the structural evolution for increasing number of bilayers ͑N͒ of a ML. 7 In the present work, we report on the domain structure evolution in AFcoupled Co/ Cu ML stacks as observed from neutron scattering measurements. These MLs show a high degree of morphological vertical correlation and small lateral correlation of the interface roughness.…”

“…Physical properties of magnetic multilayer 1 ͑MLs͒ such as interlayer coupling 2,3 and giant magnetoresistance [4][5][6] ͑GMR͒ are not only closely related to the structure of the multilayers, i.e., interface roughness and/or the evolution of the roughness along the ML stack, 7 but depend also on the details of the magnetic domain structure. 8,9 Recent investigations by Langridge et al 8 and Paul et al 10 have demonstrated the usefulness of neutron techniques in determining the field dependence of the antiferromagnetically ͑AF͒ coupled domain structure.…”