Mmh Marc Willekens

Interface intermixing and magnetoresistance in Co/Cu spin valves with uncoupled Co layers

The interpretation of experiments on the effect of interface intermixing on the giant magnetoresistance (GMR) effect in antiferromagnetic‐coupled multilayers can be complicated by the fact that interface intermixing also changes the coupling strength; therefore, we have grown an artificially intermixed region in Co/Cu spin valves with uncoupled Co layers. The structure we used was a newly engineered spin valve composed of 100 A Co+6 A Ru+25 A Co+40 A Cu+100 A Co. Here the Ru layer provides an antiparallel alignment of the Co layers and the Cu layer decouples the upper two Co layers. An intermixed CoCu region has been grown at the Cu/Co interface and in some cases also at the Co/Cu interface by alternately sputtering 1 A Co and 1 A Cu. X‐ray measurements confirm the existence of an intermixed region, although no reduction of magnetic moment is observed as is reported for homogeneous sputtered Co0.5Cu0.5 alloys. This indicates the existence of Co clusters in the intermixed regions. There is no difference in...

Magnetic and Transport Behavior of Af-Coupled Layers with a Limited Number of Repetitions

We investigated the magnetization behavior of [(Co/Pd)4-Ru]x samples with perpendicular anisotropy and a limited number of repetitions (x=1,..22). In these systems the Co/Pd multilayers behave as single magnetic entices. A detailed analysis and comparison of the magnetization curves observed by MOKE and VSM permits us to observe the magnetization reversal and hysteresis of the individual layers and to determine the antiferromagnetic coupling J between each pair of layers. A gradual increase in J is observed in all samples when going from the bottom layer to the top layer. Magnetoresistance curves show the same sharp transitions as the magnetization curves. A clear distinction can be made between an outer layer and an inner layer. These results will be compared with model calculations.

Analysis of scattering lengths in Co/Cu spin valves using a Ru barrier

Abstract The giant magnetoresistance of Co/Cu spin-valves containing a shifting Ru barrier has been investigated. The Boltzmann approach has been applied to predict how microscopic scattering lengths may be evaluated from the experiments. From the comparison of these data with the macroscopic conductivity no evidence could be found for a considerable contribution of bulk spin-dependent scattering.

Interface-selective determination of spin-dependent scattering

Spin-valve structures on top of which a thick non-magnetic back layer is deposited are introduced as a straightforward experimental tool to detect unambiguously the presence of an interfacial contribution to spin-dependent scattering for giant magnetoresistance. The interface-selectivity is evidenced by an analytical treatment of the Boltzmann equation and is illustrated in both Co/Cu/Co and Ni80Fe20/Cu/Ni80Fe20 spin-engineered structures.

Effects of Interface Intermixing on the Magnetoresistance of Spin Valves with Uncoupled Co-Layers

We have studied the effect of an artificially intermixed region grown at the interfaces of Co/Cu spin valves with uncoupled layers. Two different structures are used: exchange-biased spin valves and engineered spin valves in which two layers are antiferromagnetically coupled and a third layer, on top of this system, is not coupled to the other two. It is shown that structural effects, induced by variation of the deposition parameters and by the intermixing can play an important role. Since the present study uses sputtered layers an intrinsic initial intermixing of 4-5 angstrom is already present. For both types of spin valves Gp, ΔG and ΔR/R all show a gradual decrease when the nominal thickness of the total intermixed region is enlarged from 0 to 36 angstrom. Also when the initial degree of intermixing is decreased by sputtering at higher Ar-pressure, Gp, ΔG and ΔR/R still show a gradual decrease as a function of intermixed layer thickness. Combined with the fact that there is no difference between an intermixed region of thickness t at one Co/Cu interface or intermixed regions of thickness t/2 at two interfaces, this indicates that the electron scattering in the intermixed region is predominantly spin independent, although this region preserves a magnetic moment.

The Giant Magnetoresistance Effect

In 1986 for the first time antiferromagnetic (AF) exchange coupling was observed [1] between two metallic 100A Fe layers across a thin nonmagnetic 8A Cr layer. Due to this antiferromagnetic coupling the magnetization directions of the magnetic layers can switch between parallel and antiparallel upon the application of an external magnetic field, which is a necessary requirement to obtain the GMR effect discovered two years later, first in Fe/Cr multilayer systems [2] and thereafter in an Fe/Cr/Fe sandwich [3]. Since that time the GMR effect is extensively investigated and is widely observed in samples of well chosen layer composition and layer thicknesses whenever there exists the possibility to transfer a state where all magnetization directions of the layers are aligned parallel (P) towards a state where they are aligned antiparallel (AP). In Fig. 1 the direct relation between the magnetization vectors and the corresponding resistance is clearly illustrated in a system of 2 Co/Pd magnetic multilayers, coupled antiferromagnetically by an 8A Ru spacer layer. The AP state of the magnetization vectors at low fields corresponds to a high resistance, which transforms into a low-resistive state by the application of a magnetic field. For a general angle α between 2 magnetization vectors one may express the resistance as:

Enhanced giant magnetoresistance in spin-valves sandwiched between insulating NiO

R(\alpha ) = {{R}_{0}} + \Delta R(1 - \cos \alpha )/2

Analysis of scattering lengths in Co/Cu/Co and Co/Cu/Co/Cu spin-valves using a Ru barrier

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