4th INTERNATIONAL WORKSHOP ON ELECTRODEPOSITED NANOSTRUCTURES 16-18 March 2006, Dresden, Germany	ABSTRACTS

GIANT MAGNETORESISTANCE (GMR) IN (ELECTRODEPOSITED) MAGNETIC NANOSTRUCTURES Imre Bakonyi Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences H-1525 Budapest, P.O.B. 49, Hungary E-mail: bakonyi@szfki.hu At the first and second EDNANO meetings, we discussed experimental results which enabled us to reveal that the strongly non-saturating behaviour of the field-dependence of the GMR of electrodeposited multilayer films originates from the presence of superparamagnetic (SPM) regions in the magnetic layers. A new procedure has also been presented how to separate the SPM contribution to the GMR from the conventional ferromagnetic GMR contribution. Since then, we identified a physical model elaborated originally for granular metals [1,2] that could be well adapted for the case of electrodeposited multilayers [3]. This represents a significant progress in understanding the underlying physical processes. In the present contribution, we intend to give a description of the spin-dependent scattering processes occurring in various magnetic nanostructures which form the basis for explaining the phenomenon of GMR. The two limiting cases are (i) classical granular metals in which nanoscale non-interacting ferromagnetic (FM) particles with SPM characteristics are embedded in a non-magnetic matrix and (ii) perfect nanoscale metallic multilayers in which FM layers are separated by non-magnetic layers. In the first case, the field dependence of the magnetoresistance is proportional to the square of the Langevin function L(x) describing the field dependence of the magnetization where x = µH/kT with µ as the average SPM particle moment. In perfect multilayers, the field dependence of the GMR is governed by that of the antiferromagnetic coupling between the FM layers via the non-magnetic spacer layers. Due to a distribution of SPM particle size in granular metals, there may be larger particles which exhibit FM behaviour, i.e., their magnetization orientation does not fluctuate as was for the SPM state. In such cases, the GMR field dependence was found [1] to be proportional to L(x) and not to [L(x)]2 and this could be explained [2] by taking into account spin-dependent electron transport processes for electrons travelling between a FM and a SPM particle. At the other end, in magnetic/non magnetic multilayers, SPM regions can often occur and then applying the same model, we can observe a GMR term with a field dependence proportional to L(x) [3]. Besides the general overview of spin-dependent transport processes in magnetic nanostructures, we present our recent results on the GMR of electrodeposited multilayers which are discussed in terms of the above described model. [1] B.J. Hickey, M.A. Howson, S.O. Musa and N. Wiser, Phys. Rev. B 51, 667 (1995). [2] N. Wiser, J. Magn. Magn. Mater. 159, 119 (1996). [3] I. Bakonyi, L. Péter, Z. Rolik, K. Kiss-Szabó, Z. Kupay, J. Tóth, L. F. Kiss and J. Pádár, Phys. Rev. B 70, 054427 (2004).

 
 
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