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Evolution of GMR with spacer layer thickness in electrodeposited multilayers
I. Bakonyi, E. Simon, L. Péter, L.F. Kiss and Z.E. Horváth+ Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences H-1525 Budapest, P.O.B. 49, Hungary +Research Institute for Materials Science and Technical Physics, Hungarian Academy of Sciences H-1525 Budapest, P.O.B. 49, Hungary E-mail: bakonyi@szfki.hu |
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It was demonstrated in 1993 [1] that electrodeposited multilayers can also exhibit an large GMR effect and there has been an extended research activity in this field since then [2,3]. However, there have been contradictory reports on the evolution of the GMR with spacer layer thickness in such multilayers. Some authors presented data hinting at GMR oscillations, others have found a smooth variation of the GMR only.
In the present talk, we shall analyze the evolution of GMR with Cu layer thickness in Co Cu/Cu multilayers electrodeposited on Si/Cr(5nm)/Cu(20nm) substrates where the metallic buffer and seed layers were obtained by evaporation. A series of samples with a constant magnetic layer thickness of about 2.7 nm was prepared by two-pulse plating with galvanostatic/potentiostatic deposition mode whereby the Cu deposition potential was optimized to avoid Co dissolution and Co-codeposition. The Cu layer thickness varied from 0.5 nm to 4 nm in steps of about 0.1 nm. The longitudinal (LMR) and transverse (TMR) components of magnetoresistance were measured at room temperature up to 8 kOe magnetic fields. X-ray diffraction analysis revealed a strong (111) texture and the presence of satellite reflections indicated a good superlattice coherence.
By measuring both the LMR and TMR components, it could be established that up to about 1.5 nm Cu layer thickness, an anisotropic magnetoresistance (AMR) effect could only be observed (LMR > 0, TMR < 0). Afterwards, a clear GMR effect occurred (LMR < 0, TMR < 0) and its magnitude exhibited a monotonic increase with Cu layer thickness with a slight saturation when approaching 4 nm.
In order to get complementary information on the remagnetization process and the coupling between the magnetic layers, the magnetization curves were also measured for several multilayers both in the AMR and the GMR regimes.
Based on our recent progress [2] in understanding the field dependence of magnetoresistance in multilayers, we shall discuss the different behaviours reported for electrodeposited multilayers (presence or absence of GMR oscillation) in view of previous findings on multilayers prepared by physical deposition methods.
References
[1] M. Alper et al., Appl. Phys. Lett. 63, 2144 (1993).
[2] W. Schwarzacher and D.S. Lashmore, IEEE Trans. Magn. 32, 3133 (1996).
[3] I. Bakonyi and L. Péter: in: Electrochemical Society Proc. Vol. 2004-23, p. 227 (2006).
[4] I. Bakonyi et al., Phys. Rev. B 70, 054427 (2004).